Updated

Israeli troops were bracing for more border violence Monday after a day of deadly clashes with hundreds of Palestinians and their supporters who tried to surge from Syria into the Israeli-controlled Golan Heights. Syrian reports said 20 people were killed in those clashes.

Overnight, several dozen demonstrators had camped out on the Syrian side of the border but all was quiet early Monday.

Israeli troops were fixing a coil of barbed wire that protesters had cut through on Sunday to enter a trench in a buffer zone that Israel had dug after an earlier round of border violence three weeks ago.

The border was actually breached in that earlier round of unrest. On Sunday, it was not, but at human cost: Syrian TV reported that Israeli soldiers shot dead 20 people and wounded hundreds more when they opened fire to block protesters from entering the Golan, which Israel captured from Syria in 1967.

The government in Hamas-ruled Gaza ordered three days of mourning, calling the dead "martyrs of Palestine."

Israel accused the Syrian regime of instigating the border unrest to deflect attention from its brutal crackdown on opposition forces at home. The marchers passed by Syrian and U.N. outposts on their way to the frontier.

Israeli opposition lawmaker Binyamin Ben-Eliezer, a former general and defense minister, predicted the unrest would proliferate across Israel's various borders.

"There is only one solution," said Ben-Eliezer, whose Labor Party splintered, then quit the government in frustration over its failure to break a stubborn impasse in peacemaking with the Palestinians. "To recognize a Palestinian state and sit down tomorrow at the bargaining table," he told Israel Radio.

Sunday's unrest marked the anniversary of the Arab defeat in the 1967 Middle East war, when Israel captured the Golan Heights from Syria, the West Bank and east Jerusalem from Jordan, and the Gaza Strip and Sinai peninsula from Egypt in six days of fighting.

Israel returned Sinai to Egypt under a 1979 peace accord and left Gaza in 2005.

The Palestinians seek the West Bank and east Jerusalem, along with Gaza, for a future state. Syria demands a return of the Golan, a strategic plateau overlooking northern Israel that Israel has since annexed, in return for peace. Multiple rounds of peacemaking between Israel and both the Syrians and the Palestinians have failed.

After being caught unprepared last month, when hundreds of unarmed protesters entered the Israel-controlled Golan for several hours, Israel had promised a tough response to any new attempts to break through its frontiers.

Thousands of troops and police were deployed along the northern border in anticipation of unrest Sunday, equipped with anti-riot weaponry like tear gas and water cannon. The Israeli military said it used live fire only after firing warning shots into the air and issuing verbal warnings to protesters to stay away.

The recent protests have drawn attention to the plight of Palestinian refugees who fled or were expelled from homes in Israel during the war over Israel's 1948 creation. The original refugees, and their descendants, now number several million, and they demand "the right to return" to the families' former properties.

Israel opposes their repatriation because Palestinians would eventually outnumber Jews in the Jewish state. The fate of the refugees and their descendants is one of the toughest issues in any future Israeli-Palestinian peace accord.