Addressing a news conference at the end of four days of talks, Basma Kadmani, a Syrian exile living in France, said the council aimed to help topple Assad's dictatorship within six months and form a interim government thereafter.

"The political vision of the council will give a push to the escalation of the revolutionary work we are seeing," she said.

"This group, based on previous initiatives, and on what the street is demanding, is calling for the downfall of the regime with all of its limbs."

While condemning the Syrian government's repressive response to pro-democracy protests, the international community has bemoaned the lack of a unified opposition that it could talk to.

By finalizing names of its members, drawn from Syria's various political, religious and ethnic groups, the council hopes to fill that gap.

"The next step will be international recognition, and the council will act in accordance with the wishes of the Syrian people," Adip Shishakly, a member of a prominent Syrian political family, told Reuters at the end of the Istanbul meeting.

While not ruling out foreign military intervention in Syrian as more protesters call for international protection, Kadmani said the focus for now was on stepping up diplomatic and economic pressure on Assad.

Some 140 people were chosen as council members, of which 40 percent were based outside Syria, but more could be appointed later.

A list of 72 members was circulated but the names of those inside Syria were mostly withheld to protect them from reprisals by Assad's security forces.

FRESH VIOLENCE

Islamists, including members of the Muslim Brotherhood, were chosen alongside leftists, nationalists and independents, while all of Syria's religious and ethnic groups were represented.

Assad's government has become increasingly isolated internationally, having failed to introduce substantive reforms while using force against its own people to quell the demonstrations.

Addressing the Arab League in Cairo on Tuesday, Turkey's Prime Minister Tayyip Erdogan said he no longer trusted his former friend Assad.

On Wednesday hundreds of soldiers, backed by dozens of tanks, stormed towns and villages near Syria's northwest border with Turkey. Activists said at least four villagers were killed.

The United Nations said on Monday that 2,600 people had been killed in the violence. The president of the U.N. Human Rights Council on Thursday urged Syria to cooperate with an international probe into possible crimes against humanity committed during Syria's crackdown.

U.N. human rights investigators, who carried out a preliminary assessment in the region but were not allowed into Syria, said in a report on August 18 that the government's crackdown might be grounds for prosecutions at the International Criminal Court. They said they had evidence against 50 suspects.

A Syrian government official said this week that reports of mass killings of civilians were exaggerated and that 700 soldiers and police had been killed by "terrorist groups" and a similar number of what she described as mutineers.

Having struggled to agree the composition of the council at past meetings, the opposition was now looking to move forward with more purpose.

"In terms of external actions, the council will be seeking to fill the vacuum identified by the international community, as an alternative to Assad's regime and represent the position of the Syrian revolution in an efficient and credible way," Yaser Tabbara, a Chicago-based lawyer, who was in the steering committee for the council and was named among its members.

"We're really concerned with the demands of the people inside Syria, and we'll seek a meaningful dialogue with those inside on the next step that they want us to take," Tabbara said.

He said that the opposition has had unofficial contact with foreign governments and expected that, with the formation of the council, meetings with European and Arab governments would follow, as well as consultations with the United Nations, Arab League and Organization of the Islamic Conference.

A Canadian foreign ministry official attended the opposition meeting in Istanbul as an observer, Tabbara said.