Tens of thousands packed Tahrir Square on Tuesday to protest a power grab by Mohamed Morsi, piling pressure on Egypt's Islamist president as he faces his most divisive crisis since taking power in June.

The huge turnout in the iconic square in the heart of Cairo, as well as in the Mediterranean city of Alexandria and most of Egypt's 27 provinces, marked the largest mobilization yet against the president.

A car bomb hit a police checkpoint in a town southwest of Damascus on Tuesday morning, as the army deployed in large numbers nearby in a bid to suppress insurgents there, a monitoring group said.

"A car bomb exploded at dawn, targeting a military police checkpoint in Jdeidet Artouz," said the Syrian Observatory for Human Rights. "This was followed by intense shooting, as regular troops continued to be deployed in the fields between Kfar Sousa and Daraya."

Car bombs killed four people in Kurdish areas of the disputed northern Iraqi city of Kirkuk on Tuesday, while roadside bombs killed two more in a nearby Arab town, a security official and a doctor said.

The attacks come a day after top security officials from the federal government and Iraq's autonomous Kurdistan region reached an agreement aimed at easing high tensions in disputed areas of northern Iraq, which the country's parliamentary speaker has warned could lead to civil war.

Saudi authorities on Tuesday beheaded two nationals for murder, including one who stabbed his wife to death and burned her corpse, the interior ministry said.

Ali Mohammed Mahrazi was convicted of stabbing his wife Hunayna Khabrani repeatedly before he "poured kerosene on her body and set it on fire until it was charred," the ministry said in a statement carried by SPA state news agency.

The remains of the late Palestinian leader Yasser Arafat were reburied on Tuesday after samples were taken to be tested for signs he was poisoned, Palestinian sources said.

"The operation is finished, the tomb has been resealed and the samples have been given to the French, Swiss and Russian experts," officials from the Palestinian commission investigating Arafat's death told Agence France Presse.

Prime Minister Benjamin Netanyahu's Likud faction shifted further to the right on Monday, with the more moderate members of the ruling party faring poorly in a primary vote ahead of January elections.

The two-day poll, extended from Sunday after technical failures in the computerized system caused significant delays, ended on Monday night with nearly 60 percent of the Likud's 123,000 members casting their vote.

U.N. chief Ban Ki-moon called Monday for renewed efforts to achieve a two-state solution in the Middle East following last week's ceasefire between Israel and Hamas.

"More than ever, we need a negotiated two-state solution ending the occupation and the conflict," he said at the inauguration of a new center for interreligious dialogue in Vienna.

Gunfire from Syria hit the Israeli-occupied Golan Heights overnight close to an Israeli military vehicle monitoring the ceasefire line but causing no injuries, the military said on Monday.

"There was gunfire near an Israeli military vehicle which was driving along the security fence," a military spokeswoman said, adding the incident had occurred late on Sunday.

A U.S. announcement that a conference on a Middle East free of nuclear weapons cannot be held as foreseen is a "serious setback," Iran said Monday, accusing Washington of protecting Israel.

"The U.S. cannot unilaterally decide for the sake of Israel to announce that the conference cannot be held. This is a very serious setback for the non-proliferation regime,"Iran's ambassador to the U.N. atomic agency told Associated France Press.

Iranian warships will return to Sudan on Friday, the armed forces said, one month after a similar port call followed Khartoum's accusation that Israel bombed a military factory.

Sudan's links to Iran have come under scrutiny after Khartoum accused Israel of the October 23 strike against the Yarmouk compound, which led to speculation that Iranian weapons were stored or manufactured at the factory in Khartoum.