Twenty people were reported killed and a dozen critically wounded after Israeli troops opened fire Sunday at a crowd of pro-Palestinian protesters trying to break into the Israeli-controlled Golan Heights from neighbouring Syria.

A small group of the protesters, most of them young men, cut through coils of barbed wire along the frontier, entered a buffer zone and crawled toward a second, final fence guarded by Israeli troops.

They took up position in a trench in the buffer zone — the Associated Press said it was about 20 metres from the Israeli border, though an Israeli military spokesman later said the demonstrators got no closer than 150 metres.

Pro-Palestinian protesters try to rescue a wounded man on Sunday after he was shot by Israeli troops along the border between Israel and Syria near the village of Majdal Shams in the Golan Heights. Ariel Schalit/Associated Press

Israel says its soldiers fired warning shots in the air and orally cautioned the demonstrators before any bullets were directed their way. But starting during the day, Israeli troops periodically opened fire at the young activists jumping into the ditch, sending puffs of soil flying into the air. As the standoff stretched into the evening and the crowd on the Syrian side swelled to an estimated 1,000 people, Israeli forces fired heavy barrages of tear gas to break up the assembly.

State-run Syrian TV said 20 people were killed and 325 injured, 12 critically. Hospital officials in the border town of Quneitra confirmed those figures.

The protests marked the 44th anniversary of the Arab defeat in the 1967 Six-Day War with Israel.

Lt. Col. Avital Leibovich, an Israeli military spokeswoman, said protesters at the fence were given warnings, "but they chose instead to clash with the soldiers."

There was no Syrian comment on why the protesters were allowed to storm the border, apparently undisturbed by authorities. But Syria's state-run media portrayed the event as a spontaneous uprising of Palestinian youths from a nearby refugee camp. Around half a million Palestinian refugees live across 13 camps in Syria, a country with a population of 23 million.

Last month, thousands of Arab protesters surged to Israel's borders with Syria, Lebanon, the Gaza Strip and the West Bank for another key anniversary, Israel's 1948 creation, which demonstrators refer to as the "nakba" or "catastrophe." As many as 15 people died in border clashes with Israeli and possibly Lebanese security.

Israeli Prime Minister Benjamin Netanyahu on Sunday reiterated that he had instructed Israeli security forces to "act with resolve" but also with "maximum restraint" to guard borders and civilians.

Critics have accused Syria of deliberately stoking pro-Palestinian sentiment and encouraging Golan Heights protests to distract international attention from a bloody crackdown on internal revolts against President Bashir al-Assad.

To mark the Arab-Israel war in 1967, Palestinians in Lebanon staged strikes in all of the country's 12 refugee camps. Lebanese authorities had declared the area around the shared border with Israel a closed military zone to prevent a planned border march.

With files from The Associated Press