Syrian state media says at least 23 people have been killed and 350 more wounded after Israeli forces opened fire along the frontier to disperse pro-Palestinian demonstrators attempting to enter the Israel-occupied portion of the Golan Heights.
The official SANA news agency quoted Wel al-Halki, the country's health minister, as saying the dead included a woman and a 12-year-old boy.
The reported deaths occurred as the protesters marching from the Golan Heights approached the Israel-occupied area on Sunday. The day is observed as "Naksa Day" or "Day of Defeat" by many, marking the 44th anniversary of the 1967 war, when Israel occupied the area.
"Anyone who tries to cross the border will be killed," Israeli soldiers reportedly shouted through loudspeakers at the crowd of several hundreds.
Protesters waved Palestinian flags and threw rocks and rubbish over the fence.
Protesters, most of them young men, eventually managed to cut through coils of barbed wire marking the frontier, entering a buffer zone and crawling towards a second fence guarded by Israeli troops.
A Reuters correspondent at the scene saw at least 11 demonstrators carried away on stretchers by the crowd.
"We were trying to cut the barbed wire when the Israeli soldiers began shooting directly at us," Ghayath Awad, a 29-year-old Palestinian who had been shot in the waist, told the AP news agency.
US 'deeply troubled'
Sunday's protests were designed to draw attention to the plight of Palestinian refugees who fled or were expelled from their homes during Israel's war of independence in 1948.
Now, around half a million Palestinian refugees live across 13 camps in Syria.
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The US state department expressed its concern over the clashes, saying: "We are deeply troubled by events that took place earlier today in the Golan Heights resulting in injuries and the loss of life.
"We call for all sides to exercise restraint. Provocative actions like this should be avoided."
The US statement emphasised that "Israel, like any sovereign nation, has a right to defend itself".
Meanwhile in the occupied West Bank, skirmishes broke out at the main crossing into Jerusalem as several hundred Palestinian young people tried to approach the checkpoint.
Reacting to Sunday's incidents, Mustafa Barghouthi, an independent Palestinian politician, told Al Jazeera: "What we saw in the Golan Heights, and in front of the checkpoint to Jerusalem, were peaceful Palestinian demonstrators demanding their freedom and the end of occupation, which has become the longest in modern history.
"And they were encountered by terrible violence from Israel. They have used gunshots, tear gas, sound bombs and canisters emanating dangerous chemicals against demonstrators.
"They also beat us. I was one of those who was beaten today by the Israel soldiers today while we were peacefully trying to reach the checkpoint to Jerusalem."
Israel has accused Syrian President Bashar al-Assad of permitting the Golan protests to try to divert international attention from his bloody suppression of the popular revolt against his authoritarian rule.
Giving Israel's version of the events, Avital Leibovich, the Israeli army's spokesman, told Al Jazeera: "We [the military] saw near 12 noon an angry mob of a few hundreds of Syrians trying to reach the border fence between Israel and Syria.
"We did three steps. We first warned them verbally, we told them not to get close to the fence in order for them not to endanger their lives.
"When this failed, we fired warning shots into the air. When this failed, we had to open fire selectively at their feet in order to prevent an escalation."
The Israeli military also accused the Syrian government of instigating the protests to deflect attention from its crackdown of a popular uprising at home.
"This is an attempt to divert international attention from the bloodbath going on in Syria,'' Leibovich said.
Israel had vowed to prevent a repeat of a similar demonstration last month, in which hundreds of people burst across the border into the Golan Heights.
More than a dozen people were killed in that unrest, in which protesters had gathered to mark the 63rd anniversary of the "Nakba", to mark the expulsion of an estimated 700,000 Palestinians following Israel's 1948 declaration of statehood.