NAIROBI, Kenya - A group of Somali militants who kidnapped four international aid workers, including at least one Canadian, during an attack on a refugee camp in Kenya may have crossed the border into Somalia, Kenyan police and military officials said Saturday.

The four aid workers were kidnapped on Friday when militants ambushed a Norwegian Refugee Council convoy and killed a Kenyan driver, officials said.

The Norwegian group has not identified the nationalities of the kidnapped workers. But a security official with the case said that two of them are from Canada, one from the Philippines and one from Norway. One of the Canadian passport holders is of Pakistani origin, the security official said.

A spokesman for Foreign Affairs in Ottawa declined to comment on the report, saying Canada's top priority was "the safety and security of the citizens."

"We are pursuing all appropriate channels to seek further information and are in close contact with Kenyan authorities," Jean-Bruno Villeneuve said in an email to The Canadian Press.

"We will not comment or release any information which may compromise these efforts.''

A military commander, Philip Ndolo, said that a security escort had originally been arranged to accompany a high-ranking delegation from the Norwegian Refugee Council, but that the aid group decided at the last minute to travel through the Dadaab refugee camp without an armed escort.

Norwegian Refugee Council Secretary General Elisabeth Rasmusson was present during the attack but was not harmed or taken.

Rasmusson said Friday that the attack happened on a main road toward the city of Dadaab in "what is recognized as the safe part of the camp." She said four men with pistols carried out the attack against the two vehicles. The attackers only took one of the vehicles.

After an attack on a Doctors Without Borders convoy last year in which two Spanish women were abducted, some aid groups began using security escorts in Dadaab, a series of sprawling camps connected by sandy roads. But the Norwegian Refugee Council did not have guards on Friday.

"They had arranged the previous day (Thursday) with the understanding they would get some security officers in the morning, but for some reason they decided not to take the security officers," Ndolo said.

A Norwegian Refugee Council spokesman in Norway, Rolf Vestvik, said a risk analysis was carried out before Friday's movements through Dadaab and it was decided that it was safe for the convoy to travel.

"We wouldn't have carried out such travel if it wasn't seen as being safe," he said. "But in a situation like that there is always a risk factor and we do everything we can to minimize the risk to our staff. But if you are going to operate in areas where there are refugees you are operating in areas where there is certain risk."

Ndolo said that security officials are pursuing the attackers in an area with no mobile phone coverage, so he is waiting for an update. But, he said, it's possible the group has crossed the border.

"The vehicle was abandoned not so many kilometres from the border, so there is the possibility that if they decided to walk, with an eight hours' walk they would have been at the border, and if they made a connection with other militias they could have been picked up in a vehicle there. That is our worry," he said.

Militants have penetrated Dadaab several times over the last year. Last October gunmen kidnapped the two Spanish women from Doctors Without Borders. The two are still being held, most likely in Somalia. Several roadside bombs, most of which targeted police, have also exploded in the camp over the last year.

A spate of cross-border attacks last year, including around the resort town of Lamu, is the reason Kenya gave publicly for their military push into Somalia last October to target Islamist militants from the group al-Shabab.

_ With files from The Canadian Press

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  • FILE - In this Tuesday, July 26, 2011 file photo, then seven month old Somali boy Minhaj Gedi Farah is treated in a field hospital of the International Rescue Committee (IRC) in Dadaab, Kenya. Thousands of people, more than half of them children, died needlessly and millions of dollars were wasted because the international community did not respond to early warnings of an impending famine in East Africa, aid agencies said Wednesday, Jan. 18, 2012, even as they warned of a new hunger crisis in West Africa. (AP Photo/Schalk van Zuydam, File)

  • FILE - In this Saturday, Aug. 6, 2011 file photo, Minhaj Gedi Farah, a then seven-month-old child who arrived at the International Rescue Committee (IRC) hospital with a weight of 3.4kg on Tuesday, July 26, 2011, is photographed in the hands of his mother Asiah Dagane in the Eastern Kenyan village of Hagadera near Dadaab, 100 kms (60 miles) from the Somali border, in Kenya. In July, Minhaj was one of dozens of limp babies under mosquito net shrouds in the sweltering wards of the IRC hospital in Dadaab, the world's largest refugee camp, but after months of intensive feeding the Somali boy has the chubby cheeks and cheeky smile of most babies his age. (AP Photo/Jerome Delay, File)

  • In this photo released by the International Rescue Committee, Minhaj Gedi Farah is held in the arms of his mother Asiah Dagane in the International Rescue Committee (IRC) hospital in Dadaab, Kenya Wednesday, Oct. 19, 2011. In July, Minhaj was one of dozens of limp babies under mosquito net shrouds in the sweltering wards of the IRC hospital in Dadaab, the world's largest refugee camp, but after months of intensive feeding the Somali boy has the chubby cheeks and cheeky smile of most babies his age. (AP Photo/IRC) EDITORIAL USE ONLY

  • FILE - In this Monday, July 11, 2011 file photo, Somali parents care for their young children who are being treated for malnutrition at a Doctors Without Borders (Medecins Sans Frontieres) hospital in Dagahaley Camp, Dadaab, Kenya. Thousands of people, more than half of them children, died needlessly and millions of dollars were wasted because the international community did not respond to early warnings of an impending famine in East Africa, aid agencies said Wednesday, Jan. 18, 2012, even as they warned of a new hunger crisis in West Africa. (AP Photo/Rebecca Blackwell, File)

  • In this photo taken Monday, Feb. 20, 2012, parts of Dadaab, the world's largest refugee camp, are seen from a helicopter in northern Kenya. (AP Photo/Ben Curtis)

  • Kenya East Africa Famine

    A Somali girl waits to collect water at the UNHCR's Ifo Extension camp, outside Dadaab, eastern Kenya, 100 kilometers (62 miles) from the Somali border, Wednesday, Aug. 10, 2011. The Dadaab refugee camp - the largest in the world - was built for 90,000 people. The current population is over 400,000 with thousands of new arrivals crammed into areas outside the refugee camp, waiting to be formally admitted. (AP Photo/Jerome Delay)

  • A woman carries three water containers on her back to her home at a refugee camp in Dadaab, Kenya, Thursday, Aug 4, 2011. Dadaab, a camp designed for 90,000 people now houses around 440,000 refugees. Almost all are from war-ravaged Somalia. Some have been here for more than 20 years, when the country first collapsed into anarchy. But now more than 1,000 are arriving daily, fleeing fighting or hunger(AP Photo/Schalk van Zuydam)

  • Women stand in line to get water in a refugee camp in Dadaab, Kenya, Thursday, Aug 4, 2011. Dadaab, a camp designed for 90,000 people now houses around 440,000 refugees. Almost all are from war-ravaged Somalia. Some have been here for more than 20 years, when the country first collapsed into anarchy. But now more than 1,000 are arriving daily, fleeing fighting or hunger(AP Photo/Schalk van Zuydam)

  • People at a refugee camp in Dadaab, Kenya, Thursday, Aug. 4, 2011. Dadaab, a camp designed for 90,000 people now houses around 440,000 refugees. Almost all are from war-ravaged Somalia. Some have been here for more than 20 years, when the country first collapsed into anarchy. But now more than 1,000 are arriving daily, fleeing fighting or hunger(AP Photo/Schalk van Zuydam)

  • Adam Ibrahim from Somalia plays with his father Abdulle Ibrahim's cell phones at the International Rescue Committee, IRC, in Dadaab, Kenya, Wednesday, Aug 3, 2011. Dadaab, a camp designed for 90,000 people now houses around 440,000 refugees. Almost all are from war-ravaged Somalia. Some have been here for more than 20 years, when the country first collapsed into anarchy. But now more than 1,000 are arriving daily, fleeing fighting or hunger.(AP Photo/Schalk van Zuydam)

  • Malnourished Somalian refugees sit outside a field hospital of the International Rescue Committee, IRC, in Dadaab, Kenya, Wednesday, Aug 3, 2011. Dadaab, a camp designed for 90,000 people now houses around 440,000 refugees. Almost all are from war-ravaged Somalia. Some have been here for more than 20 years, when the country first collapsed into anarchy. But now more than 1,000 are arriving daily, fleeing fighting or hunger.(AP Photo/Schalk van Zuydam)

  • Woman refugees sit inside a food distribution center run by the World Food Programme (WFP), in the town of Dadaab, Kenya, Tuesday, Aug 2, 2011. Dadaab, a camp designed for 90,000 people now houses around 440,000 refugees. Almost all are from war-ravaged Somalia. Some have been here for more than 20 years, when the country first collapsed into anarchy. But now more than 1,000 are arriving daily, fleeing fighting or hunger.(AP Photo/Schalk van Zuydam)