Syrian President Bashar Assad was lying when he denied his regime had any involvement in the massacre of more than 100 civilians near the central town of Houla, the White House said Monday.

Asked if Assad lied at the weekend when he denied his forces fired on innocent civilians near Houla, President Barack Obama's spokesman, Jay Carney, said: "Yes.

Egyptian politicians, including three of the losing candidates in the first round of the presidential election, joined forces on Monday with youth groups demanding the suspension of a second-round runoff.

The joint call is aimed at putting pressure on election frontrunner Ahmed Shafiq, a former Hosni Mubarak premier, who is due to square off against Muslim Brotherhood candidate Mohammed Mursi on June 16-17.

A Syrian opposition group announced Monday that they are creating a new military structure consisting of 12,000 fighters to topple the regime of the Syrian President Bashar Assad.

"We announce today the unification of all fronts in a single center to bring about the collapse of the oppressing regime," Khaled al-Okla from the Syrian Revolutionaries Front (SRF) read from a statement at a press conference.

Slovakia said Monday it has summoned the Syrian ambassador over recent violence in Syria, particularly the Houla massacre, which claimed 108 lives including those of 49 children, according to UN figures.

"The ministry is deeply concerned about the continuous violation of human rights in Syria and calls for an early and full implementation of the peace plan of international envoy Kofi Annan," the Slovak foreign ministry said in a statement.

Syrian President Bashar Assad is determined to crush the rebellion against his regime, even at the cost of triggering a civil war in the country, bolstered by support from Moscow, analysts say.

"He has been ready to fight to the end right from the start and as long as he has Russia's support he believes he will win," Middle East expert Agnes Levallois told Agence France Presse.

A Turkish court is to hold on November 6 the first hearing of a trial against four Israeli commanders held responsible for a deadly flotilla raid in 2010, Anatolia news agency reported Monday.

The date was announced by the Istanbul court two weeks after it unanimously approved an indictment by Turkish prosecutors, who want life sentences for the Israelis for their alleged role in the deadly maritime assault, the agency said.

Hundreds of young settlers began marching from a West Bank outpost to Jerusalem on Monday to protest against plans to raze five homes built on private Palestinian land.

Around 400 flag-waving demonstrators joined the march, which began at the so-called Ulpana neighborhood on the edge of the Beit El settlement, and was to end in Jerusalem on Tuesday evening, with a mass rally outside parliament planned for Wednesday, organizers said.

A militia of Libyan ex-rebels entered Tripoli International airport with tanks and armored vehicles and completely blocked air traffic on Monday, a day after their leader was arrested, officials said.

"It is total confusion. Everyone is fleeing. Several armored vehicles and tanks are positioned on the tarmac, blocking traffic," an official at the airport told Agence France Presse.

Saudi Arabia's public prosecutor on Monday accused prominent activist Waleed Abu Alkhair of "disrespecting" the judiciary and contacting foreign organizations, his wife told Agence France Presse by telephone.

Alkhair was summoned by the prosecutor in the Red Sea city of Jeddah who accused him of "disrespecting the judiciary system... contacting foreign organizations and signing a petition demanding the release of detainees," some of whom are being held over terror links, Samar Badawi said.

Arab League chief Nabil al-Arabi is to head to New York later this week for talks on Syria with U.N. chief Ban Ki-moon, a League official said on Monday.

"Arabi's four-day visit, starting on Thursday, will focus on the Syrian crisis and on efforts to convince the U.N. Security Council of the need for an urgent solution," the official added.