Islamist fighters now control much of the frontier on the Syrian side of the Golan Heights, according to Israel's military. There has been heavy fighting between the rebels and Syrian government forces in the past week.
The Islamists come from the Nusra Front, a Syrian rebel group linked to al-Qaeda. They still hold more than 40 United Nations peacekeepers seized last week.
Israel's military is keeping an especially close watch on the Golan Heights, monitoring the moves made by the Nusra Front while also tracking the more extreme group, Islamic State in Syria and Iraq (ISIS).
An Israeli officer told the newspaper Haaretz that there is no sign of ISIS near the Golan Heights. "But they might show up later on," he said. (http://www.haaretz.com/news/middle-east/.premium-1.613760)
The Nusra Front took control of the Quneitre crossing last week, used as a transit point for United Nations peacekeepers and some goods, such as apples, to market in Syria. Syrian government forces have launched attacks to push the rebels from their positions.
Several tank shells and mortar rounds from Syria have landed in the Israeli Golan Heights in the past two weeks. An Israeli soldier was wounded last week in one incident. The Israel Defence Forces has retaliated by striking several Syrian military positions.
The escalation has Israeli residents of the Golan on edge.
"Yes, we're worried but living in this part of the world you're walking on a tinder box," Mark Reitkopp told me as we stood on a hill overlooking Syria. "But hopefully, things will try to straighten themselves out."
Reitkopp, who lives in the settlement of El Rom, said he can often hear the fighting in Syria, about a kilometre away from his home. The violence has forced his kibbutz to suspend the apple harvest on land adjacent to the Syrian frontier.
The flare-up in fighting on the Syrian side of the Golan Heights came just as Israel agreed to a ceasefire with Hamas, ending a 50-day war in the Gaza Strip. Israel's military has redeployed tanks and troops from it southern border with Gaza to the Golan. Convoys of military transports carrying tanks, armoured personnel carriers snaked their way up the hills into the area earlier this week.
"We have already taken steps," to prepare for the threat posed by the Nusra Front, said Israeli Prime Minister Benjamin Netanyahu. "We are prepared for various possibilities.
"But this bears out what I have been saying: we live in a tough Middle East, in a tough area, and compared with other countries, we are taking care of our security and economy better than everyone."
Netanyahu has said Israel has no interest in being drawn into the Syrian civil war, which has raged for more than three years now. Any serious attacks by Syrian rebels on Israel, however, would be met with an intense response from Israel's military. The Israeli air force is believed to have carried out several strikes on arms shipments destined for the Lebanese militant group Hezbollah.
The increased fighting recently has made some of the hilltop viewing areas in the Israeli Golan Heights popular tourist destinations.
Canadian Laurie Conn-Zuckerman, along with her husband and daughter, visited the lookout over the Syrian town of Quneitre earlier this week, she says, to see the threat posed to Israel every day.
"We live in a bit of a bubble in Toronto, and I think it's really important for everyone in the western world who cherishes our freedom to experience a little bit of what it's like to live every day in a country that you have to be on your toes all the time," she told me.
Conn-Zuckerman said she believes the threat from Islamist groups will only grow, adding that Canada should be doing more to stop the rise of these insurgents.
"I think if we had to send out troops in to fight for democracy, I would support that."
For Israelis who live in the Golan, they have spent the last three years living on the doorstep of Syria's bloody civil war. Those I spoke to were not overly concerned about the advance of the Nusra Front in the area. The rise of ISIS, however, is another story.
"There are extremists and there are extremists," said El Rom resident Mark Reitkopp. "With ISIS, I'd be much more worried if they were at Quneitre rather than the ones that are waving their black flag right now."