DAMASCUS  - Syria’s main opposition group is pulling out of international talks and demanding world action to stop the slaughter of Syrians, officials said Saturday, as missiles killed dozens in the second city of Aleppo.The Syrian National Coalition’s decision to boycott talks with world power came after it said it would form a government to run “liberated areas” of Syria. “We cannot continue listening to statements that are not accompanied by action,” the opposition umbrella group’s spokesman Walid al-Bunni said in remarks to France 24’s Arabic-language channel on Saturday. “The world has a responsibility to protect (the Syrian people) from a butcher who has been slaughtering them for two years,” a reference to President Bashar al-Assad.Coalition chief Ahmed Moaz al-Khatib repeated the call for concrete action on Syria at a demonstration in Cairo. “All the administrations of the world can see what is happening... We cannot visit any country until there is a clear decision on this savage, aggressive regime,” Khatib told the Dubai-based Al-Aan pan-Arab television.Late on Friday, the group had said it would not attend meetings in Italy, Russia and the United States to protest the “shameful” lack of global condemnation of “crimes committed against the Syrian people”. It had been due to attend the Friends of Syria meeting in Rome on Thursday, and Khatib had also been invited to Moscow. “The international silence on the crimes committed every day against our people amounts to participating in two years of killings,” a statement said. “We hold the Russian leaders in particular ethically and politically responsible because they continue to support the (Damascus) regime with weapons.” Bunni also challenged the United States to honour what he said were promises of support for democracy in Syria. “Our visit to Washington is on hold until Washington takes a stance that is in accordance with US statements on its support for democracy,” the opposition spokesman said. On Friday, he had announced plans for a government for “liberated areas” that he said he hoped would be based inside northern Syria. On Saturday, Britain urged the opposition to reconsider its decision to pull out of the Rome, Washington and Moscow meetings, insisting “now is not the time to give up” on talks. “The UK is preparing a further offer of support to the National Coalition in Rome, and we are urging them to reconsider their decision,” a Foreign Office spokeswoman told AFP.Meanwhile, peace envoy Lakhdar Brahimi said Thursday’s attack in Damascus had left about 100 people dead and wounded another 250. Describing it as a “war crime”, the UN-Arab League envoy said “nothing could justify such horrible actions that amount to war crimes under international law.” European Union foreign policy chief Catherine Ashton also condemned “such brutality that killed so many people, mostly civilians, including children.” Both the regime and opposition have blamed “terrorists” for the attack near the ruling Baath party’s main offices. The same day, another 22 people were killed in a triple bombing targeting security headquarters in northern Damascus, said the Syrian Observatory for Human Rights. In Aleppo, at least 37 people, including 19 children, had been killed and 150 wounded when three missiles hit the Tariq al-Bab district on Friday, said Observatory director Rami Abdel Rahman.Shelling of the city’s Maadi district caused a building to collapse, killing an unknown number of people, and rebels fought troops near Aleppo international airport and Nayrab and Kwayris air bases, the Britain-based group said.The army’s use of surface-to-surface missiles is part of a bid to advance on Aleppo, swathes of which the rebels have seized since mid-2012, said Abdel Rahman. A security official in Damascus said late last year that missiles of the type being used in Aleppo were a Syrian-made version of Scuds, while Nato has reported the use of ballistic missiles in the country. Elsewhere in Aleppo, shelling on the Maadi district of Aleppo caused a building to collapse, said the Observatory. An unknown number of people were killed there, it added. In the province, rebels fought troops on Saturday morning near Aleppo international airport and Nayrab air base, southeast of the provincial capital, said the Observatory.Some 70,000 people have been killed in Syria’s nearly two-year war, the UN says. On Saturday, around 150 Kurdish women in the war-wracked northern Syrian province of Aleppo have set up a fighting battalion, a monitoring group said. “The Kurdish popular committees have set up the first women’s battalion, comprising some 150 women fighters. The battalion is named the Martyr Rokan Battalion,” said the Syrian Observatory for Human Rights.