Syrian opposition groups called Thursday for President Bashar al-Assad's immediate resignation, in a joint declaration at the end of a two-day meeting in Turkey.

The statement, read out in Arabic in the Mediterranean resort of Antalya, urged the "immediate resignation of President Bashar al-Assad from all functions he occupies" and asked him to "leave his powers to a vice-president," without specifying whom it was referring to.

U.S. Secretary of State Hillary Clinton said Thursday that the international community needs to be more united on dealing with the Syrian government's crackdown on the pro-democracy movement there.

"Right now the attitude of the international community is not as united as we are seeking to make it," the chief U.S. diplomat told reporters.

Israeli Prime Minister Benjamin Netanyahu's office on Thursday denied reports of a breakthrough in negotiations to free Gilad Shalit, an Israeli soldier captured by Palestinian militants in Gaza in 2006.

Netanyahu's office issued the statement after Egyptian newspaper El-Mesryoon reported that a deal to free Shalit in exchange for 1,000 Palestinian prisoners would be completed within hours.

French writer Bernard Henri Levy said he delivered a message on Thursday from Libyan rebel leaders to Israel's premier saying they would seek diplomatic ties with Israel if they came to power.

Levy told Agence France Presse he passed on the verbal message from Libya's National Transitional Council during a 90-minute meeting with Israeli Prime Minister Benjamin Netanyahu in Jerusalem.

Security forces armed with heavy machine-guns shot dead 15 civilians in Rastan in the Homs region of central Syria on Thursday, a human rights activist said.

"Fifteen civilians were killed by heavy machine-gun fire in the town," the activist said, adding he had a list of the names. Security forces had sealed off the town, cutting off outside aid.

Deadly fighting raged between armed tribesmen and security forces on the streets of Sanaa Thursday, sending thousands of residents fleeing and closing the Yemeni capital's airport, witnesses said.

Medics said bodies were lying in the streets of al-Hasaba neighborhood, bastion of powerful tribal leader Sheikh Sadiq al-Ahmar, where the fighting erupted on Tuesday after a truce broke down.

France is ready to host a Middle East peace conference before the end of July to help re-launch stalled negotiations, France's Foreign Minister Alain Juppe said on Thursday.

Speaking in Ramallah, Juppe warned that the current stalemate between Israel and the Palestinians was "untenable" and said France was willing to transform a July meeting of international donors into a broader peace conference.

Protesters, armed for the first time since demonstrations began in January, clashed Thursday with security forces in the flashpoint city of Taez, witnesses told Agence France Presse.

Witnesses said the clashes took place near the presidential palace and near a post held by the Republican Guard, an elite army unit loyal to embattled President Ali Abdullah Saleh and led by his son Ahmed.

Six Israeli police officers and five settlers were injured early Tuesday morning in violent clashes that erupted as police dismantled an illegal settlement outpost, a police spokesman told Agence France Presse.

Police moved in to the Ali Ayan outpost in the West Bank north of Ramallah in the early hours of Tuesday morning, police spokesman Micky Rosenfeld said.

Syrian opposition groups insisted on regime change as they met in Turkey on Wednesday, a day after President Bashar Assad decreed an amnesty for political prisoners following two months of bloodshed.

The three-day gathering -- titled "Conference for Change in Syria" -- opened with the Syrian national anthem and a minute of silence for "the martyrs" killed in bloody crackdowns on street protests simmering in Syria since March.