Israeli soldiers fired on Syrian protesters trying to breach the border in the frontier of Golan Heights on Sunday, leaving at least 20 people dead and hundreds wounded.
Hundreds of Syrian activists, joined by Palestinians, approached the border to mark the anniversary of the Six Day War.
A 12-year-old boy was among the dead, while 220 people were reported injured, according to unconfirmed reports on Syrian state TV.
As the activists marched on the trench and barb-wire line that separates the Israeli-controlled Golan Heights from Syria, Israeli forces had warned them to turn away.
The Israeli soldiers "shouted at them, warned them to stop and that they were endangering their lives if they pressed forward," CTV's Martin Seemungal, reporting from Ramallah in the West Bank, told Â鶹´«Ã½ Channel.
When Israeli forces opened fire, many demonstrators panicked and ran, but dozens more continued heading toward the trench, shouting "shahid," or "martyr."
The Israeli military, expecting that the anniversary of the Arab defeat in the 1967 war would spark unrest, was under orders to use "maximum restraint," said Seemungal. Israel had hoped to avoid a repeat of last month's bloodshed, when border clashes left 12 dead and saw thousands of troops mobilized as protestors marked the anniversary of the formation of the Jewish state in 1948.
"There was an order from the chief of the Israeli Defense Force that they would try not to use lethal ammunition -- that they would fire into the air, fire tear gas and rubber bullets -- and as a last resort they would shoot at the lower part of the body," said Seemungal. "So it's very unclear how these deaths actually happened."
A separate clash on Sunday between some 80 Palestinians and Israeli forces in the West Bank ended with tear gas being fired into the crowd, he noted.
Israel is blaming the incident on Syria, accusing its neighbour to the north of trying to divert attention from its violent crackdowns on internal unrest.
"This is an attempt to divert international attention from the bloodbath going on in Syria," said Lt.-Col. Avital Leibovich, an Israeli military spokesperson.
"In the end, we are guarding our border," she said. "I wish they had obeyed our verbal warnings, but they chose instead to clash with the soldiers."
The Golan Heights -- together with the Sinai Peninsula, east Jerusalem, the Gaza Strip and the West Bank -- were seized by Israel during its 1967 war with Egypt, Syria and Jordan.
Things were relatively calm on Israel's other borders on Sunday.
About 400 Gazans hoisting Palestinian flags and posters calling for an end to the occupation gathered about three kilometres from the main passenger crossing into Israel. But dozens of Hamas riot police prevented them from marching toward the crossing.
With files from Associated Press
