Harper says there is evidence that Hamas, listed by Canada as a terrorist organization, is using human shields in its attempts to stave off the Israeli offensive.
"The indiscriminate rocket attacks from Gaza on Israel are terrorist acts, for which there is no justification," Harper said in a statement issued Sunday.
"It is evident that Hamas is deliberately using human shields to further terror in the region."
Harper also called on other world leaders to rally behind Israel as it tries to prevent rockets being fired from Gaza into its territory.
Silence, he suggested, would only embolden Israel's attackers.
"Failure by the international community to condemn these reprehensible actions would encourage these terrorists to continue their appalling actions," Harper said.
"Canada calls on its allies and partners to recognize that these terrorist acts are unacceptable and that solidarity with Israel is the best way of stopping the conflict."
Harper's statements came as Israel briefly deployed ground troops inside the Gaza Strip.
Israel had earlier warned northern Gaza residents to evacuate their homes as the six-day offensive that has killed more than 160 Palestinians was widened.
The United Nations Security Council and others have called for a ceasefire but the attacks have only escalated as Israel masses tanks and soldiers at Gaza's borders.
Israel widened its range of Gaza bombing targets Saturday to include civilian institutions with suspected Hamas ties. One strike hit a centre for the disabled, killing two patients and wounding four people. In a second attack, an Israeli warplane flattened the home of Gaza police chief Taysir al-Batsh and damaged a nearby mosque as evening prayers ended, killing at least 18 people. Fifty were wounded, including al-Batsh himself.
Harper urged the Palestinian government to disarm Hamas and other Palestinian terrorist groups operating in Gaza.
But despite forming a government with Hamas' backing last month, Palestinian President Mahmoud Abbas' influence in Gaza is minimal.
In the West Bank city of Ramallah, Abbas called on U.N. Secretary-General Bank Ki-moon to provide "international protection" for the Palestinian people.
"The situation has become unbearable _ hundreds of martyrs and thousands of wounded and huge destruction,'' Abbas said.
Early Sunday, Israeli troops launched a brief raid into northern Gaza to destroy what the military described as a rocket-launching site.
The military said the incursion left four soldiers slightly wounded.
Northern Gaza is home to at least 100,000 people.
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