Life in Gaza began returning to normal on Thursday with a public holiday to mark a ceasefire that ended a violent eight-day confrontation with the Israeli military.

After days and nights cooped up at home, their buildings rocked by an unrelenting Israeli bombing campaign and the sound of outgoing Palestinian rocket fire, residents were eager to reclaim their hometowns and their lives.

At least 40,000 people have been killed in violence across Syria since the outbreak of an anti-regime revolt in March last year, the Syrian Observatory for Human Rights said on Thursday.

"At least 28,026 civilians, 1,379 defectors, 10,150 soldiers and 574 unidentified people have been killed in Syria in the past 20 months," said Observatory director Rami Abdel Rahman.

Israeli troops arrested 55 Palestinian "terror operatives" across the West Bank overnight, hours after a truce came into effect in the Gaza Strip, the army said on Thursday.

"A total of 55 terror operatives, who are affiliated with different terror groups have been detained. Among those arrested were a number of senior level operatives," a statement said, with public radio saying it included members of Hamas and Islamic Jihad.

Rebel fighters seized the town of Mayadeen in eastern Syria on Thursday, a monitoring group said, adding that a large area on the Syrian-Iraqi border is now under control of insurgents.

"The area east of the city of Deir Ezzor, on the Iraqi border, is now the largest area in the whole country that is out of army control," said Syrian Observatory for Human Rights director Rami Abdel Rahman.

Defense Minister Ehud Barak warned on Thursday that Israel may resume its attacks on Gaza at any time if a truce that ended a week of bloodshed fails to hold.

The ceasefire "can last nine days, nine weeks or more, but if it does not hold we will know what to do, and then of course we shall consider the possibility of resuming our (military) activity in case of shooting or provocation," he told public radio.

Hamas chief Khaled Meshaal said on Wednesday that Israel had "failed in all its goals" after a Gaza truce deal came into effect, while thanking Egypt's President Mohamed Morsi for his support.

"After eight days, God stayed their hand from the people of Gaza, and they were compelled to submit to the conditions of the resistance," Meshaal said.

Israel and the United States have agreed to work together to prevent the smuggling of weapons from Iran to militant groups in the Gaza Strip, Prime Minister Benjamin Netanyahu said on Wednesday.

"Israel cannot sit idly by as its enemies strengthen themselves with weapons of terror so I agreed with President (Barack) Obama that we will work together -- Israel and the United States -- against the smuggling of weapons to terror organizations, most of which comes from Iran," he said in a televised address.

U.S. President Barack Obama thanked his Egyptian counterpart Mohamed Morsi on Wednesday for his role is negotiating a planned truce between Israel and Palestinian militants in Gaza.

"The president thanked President Morsi for his efforts to achieve a sustainable ceasefire and for his personal leadership in negotiating a ceasefire proposal," the White House said in a statement.

Bahrain's leaders pushed back against criticism by a leading rights group Wednesday that the Gulf state has failed to follow through with promised political and security reforms in the wake of the kingdom's anti-government uprising.

Authorities cited a series of measures taken since an independent report on the crisis came out last November, including giving more oversight to parliament.

Officials say Turkey has requested deployment of NATO's Patriot air defense missiles over concerns about Syria's civil war.

Turkish officials have become increasingly concerned about the civil war spilling over the border. A statement from the Turkish government said the request has been made in the "face of risks from the ongoing crisis in Syria."