Britain has urged the Syrian opposition not to give up on talks that could help end the terror in the country, after the rebels representative said they would not attend a meeting in Rome and talks in Russia and the US.

The Syrian National Coalition has withdrawn from the meetings in protest about the international "silence" on the violence in the country, including an attack this weekend which killed 29 people in Aleppo.

The umbrella opposition group with now pull out of a Friends of Syria meeting in Rome next Thursday and further scheduled talks in Washington and Moscow.

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Anti-Syrian regime protesters holding a banner during a demonstration, at Kafr Nabil town, in Idlib province, northern Syria

A Foreign Office spokeswoman said: "The UK is preparing a further offer of support to the National Coalition in Rome, and we are urging them to reconsider their decision.

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"It is important to have coalition participation, and we strongly urge members to help win the arguments for achieving more support for the opposition.

"The coalition is making progress; it is not easy, but now is not the time to give up.

"We share a common frustration about the situation in Syria and the horrors being perpetrated by the Assad regime.

"We strongly believe that the international community and the National Coalition need to work closely together to address the situation. That makes it essential that we continue to have a constructive dialogue.

"The meeting in Rome would be a useful opportunity for the coalition and ministers from key supportive countries to continue this dialogue."

A statement from the SNC singled out Russia, the BBC reported: "The international silence on the crimes committed every day against our people amounts to participating in two years of killings."

"The Russian leadership especially bears moral and political responsibility for supplying the regime with weapons."

"Hundreds of civilians have been killed by Scud missile strikes and Aleppo is being systematically destroyed."

The conflict has been grinding on for almost two years, with more than 70,000 dead and half a million refugees, a number that could double over the coming year, according to the UN's figures.

On Thursday alone more than 60 people were killed in a car bomb explosion in central Damascus, close to the headquarter's of Syrian President Bashar al-Assad's party's headquarters and the Russian embassy.

There is no apparent end in site. The Syrian National Coalition has repeatedly declared that any negotiations to end the conflict must exclude President Assad, although their position on that may be softening according to a leaked memo seen by Reuters.

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  • This photo released by the Syrian official news agency SANA, shows a Syrian fire fighter extinguishing burning cars after a huge explosion that shook central Damascus, Syria, Thursday, Feb. 21, 2013. A car bomb shook central Damascus on Thursday, exploding near the headquarters of the ruling Baath party and the Russian Embassy, eyewitnesses and opposition activists said. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows first responders working after a huge explosion that shook central Damascus, Syria, Thursday, Feb. 21, 2013. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows flames and smoke rising from burned cars after a huge explosion that shook central Damascus, Syria, Thursday, Feb. 21, 2013. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows Syrian security agents carrying a body following a huge explosion that shook central Damascus, Syria, Thursday, Feb. 21, 2013. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA shows an injured Syrian man lying on the ground after a huge explosion that shook central Damascus, Syria, Thursday, Feb. 21, 2013. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows flames and smoke rising from burned cars after a huge explosion that shook central Damascus, Syria, Thursday, Feb. 21, 2013. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows Syrian security agents carrying a body following a huge explosion that shook central Damascus, Syria, Thursday, Feb. 21, 2013. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows Syrian security agents next to a vehicle on fire following a huge explosion that shook central Damascus, Syria, Thursday, Feb. 21, 2013. (AP Photo/SANA)