Britain has formally opened talks with the Syrian opposition movement as international pressure continues to mount against the beleaguered regime of President Bashar al-Assad.

Frances Guy, a former ambassador to Lebanon, met members of the exiled opposition in Paris yesterday. The Foreign Secretary, William Hague, is to meet members of the Syrian opposition in London next week when they will also hold talks with senior officials in Downing Street.

Although the UK, along with other Western states like France – which appealed to the United Nations yesterday to impose tougher sanctions – has been in informal contact with the opposition for the last three months, the progression of the working relationship opens up the prospect of the rebels eventually being recognised as the country's representatives and supplanting the Assad regime.

The West's Libyan mission started in a similar fashion with the country's revolutionaries, but senior diplomatic sources warned against drawing parallels. "This is not about recognition of them as the government – that is not the case," said a senior diplomatic source. "The difference with the Libyan situation was that the Libyan National Transitional Council controlled swathes of the country. We are asking the Syrian opposition to present a coherent set of policies and organise themselves." The Syrian National Council and the National Co-ordination Committee for Democratic Change are among the groups whose leaders have been involved in the talks.

The development comes as France said that it, too, was ready to work with the Syrian opposition, maintaining that it is too late for the Assad regime to save itself by carrying out reforms.

Opposition from the veto-wielding members Russia and China has largely prevented the UN's Security Council from responding to Assad's crackdown on an eight-month uprising against his rule. But, following talks yesterday in Turkey, the French Foreign Minister Alain Juppé said the situation was "no longer sustainable" and that the UN must act.

"It is not normal that the Security Council has not made any decision so far," Mr Juppé told reporters. "I hope those blocking any resolution will be aware of the reality of the situation."

Turkey also called for action, with its Foreign Minister, Ahmet Davutoglu, saying more must be done to stop the "massacre".

As international pressure on Syria builds, Damascus made a tentative gesture to the Arab League, agreeing in principle to allow observers to enter the country for the first time to oversee the implementation of a peace plan to end the bloodshed.

But there were few signs yesterday that the violence was abating following reports that at least 12 civilians, including two children, were killed when security forces fired on protesters following Friday prayers.

Syria's apparent concession came after the Arab League suspended Syria and gave it until the end of this week to implement a peace plan that calls for the regime to withdraw its forces from towns and end the violence. Hundreds of people have been killed since Syria accepted, and then largely ignored, the peace plan three weeks ago.

Syrian officials were yesterday quoted as saying that they would accept foreign observers in the country, but that they had outlined their reservations to the Arab League. The body, which has threatened Damascus with sanctions, said it was studying the suggestions.

But Mr Juppé expressed scepticism that Syria was ready to stop the violence. "We believe the regime was not willing to implement a reform programme and now it is too late," he said.

The UN estimates that at least 3,500 people have been killed since the government began its crackdown against an anti-regime uprising in March. Assad's regime has accused foreign-backed "armed terrorist gangs" of killing 1,000 of its security personnel.

The soaring death toll has pushed some to demand the international community put greater pressure on the embattled regime. In what could be a preliminary push towards sanctions, Germany, France and Britain are planning to ask the UN General Assembly to adopt a non-binding resolution condemning the violence in Syria.

The European Union has already imposed sanctions on Syria, but Russia, a close ally of Syria, and China have blocked any wider international measures under a UN umbrella.