The statement Monday by UN special coordinator for Lebanon Michael Williams was unusually forceful. He said he was “shocked” by the number of deaths and urged both sides to show restraint.

Thousands of Arab protesters marched toward Israel’s borders with Syria, Lebanon and Gaza on Sunday in an unprecedented wave of demonstrations.

The ensuing clashes left at least 15 people dead, including 10 Palestinians in Lebanon.

Sunday’s clash in Lebanon was the deadliest incident along the volatile border in five years.

Meanwhile, Palestinian group Hamas on Monday denounced Israel for deadly clashes along its borders with Syria and Lebanon during “Nakba” day rallies, adding the world community must bear responsibility.

“We firmly condemn this new Zionist crime against our people who were demonstrating peacefully,” the group, which controls the Gaza Strip and whose leader Khaled Meshaal is based in Damascus, said in a statement.

“We call on the international community to assume its responsibility in light of the continuous Zionist crimes against our people,” it said, adding that Sunday’s clashes marked a new chapter in the struggle against the “Zionist occupation.” “We say to the entire world that the return of the Palestinian refugees to their homeland will remain a central part of the Palestinian question,” the statement said.

In another development, the White House accused the Syria on Monday of inciting deadly border clashes between Israeli troops and Palestinian demonstrators, saying Damascus was trying to distract attention from its own violent crackdown on protests.

White House spokesman Jay Carney expressed regret for the loss of life in confrontations on Israel’s frontiers with Syria, Lebanon and Gaza on Sunday but said the Jewish state: “has the right to prevent unauthorized crossing at its borders.” “We urge maximum restraint on all sides,” Carney told reporters on Air Force One as President Barack Obama flew to Tennessee.

The White House put the onus on the government of Syrian President Bashar Assad for the violence that broke out on the Israeli-Syrian border.

Carney said the administration was “strongly opposed to the Syrian government’s involvement in inciting yesterday’s protests in the Golan Heights.” “Such behavior is unacceptable and does not serve as a distraction from the Syrian government’s ongoing repression of demonstrators in its own country,” he said.

Meanwhile, Israel said Monday it will file a complaint with the United Nations against Syria and Lebanon after protesters from the two nations massed on its borders, with some managing to infiltrate from Syria.

“We have filed a complaint with the presidency of the Security Council and Secretary General of the United Nations against Syria and Lebanon, who are responsible for violating our borders, international agreements and UN resolutions,” foreign ministry spokesman Yigal Palmor said.

“Israel warned the United Nations and the international community that May 15 would be a volatile day and that certain individuals would attempt to engage in provocative acts of violence,” he added.

“The Syrian and Lebanese authorities did nothing to assume their responsibilities, despite having been warned.”