GENEVA, Jan 31 (Reuters) - Syria's main opposition group met U.N. mediator Staffan de Mistura for the first time on Sunday, but the peace process ran straight into trouble after Islamic State bombers killed more than 60 people near the country's holiest Shi'ite shrine.
Representatives of the Saudi-backed Higher Negotiation Committee (HNC) - which includes political and militant opponents of President Bashar al-Assad - warned they may yet walk away from the Geneva talks unless the suffering of civilians in the five-year conflict is eased.
The head of the Syrian government delegation retorted that the blasts in Damascus, which the Interior Ministry blamed on a car bomb and two suicide bombers, merely confirmed the link between the opposition and terrorism - even though Islamic State has been excluded from the talks.
The United Nations is aiming for six months of negotiations, first seeking a ceasefire, later working toward a political settlement to the civil war that has also killed over 250,000, driven more than 10 million from their homes and drawn in global powers.
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Only on Friday, the HNC said it would boycott the process, insisting it wanted an end to air strikes and sieges of Syrian towns before joining the negotiations. This forced de Mistura - who invited the government and opposition umbrella group for "proximity talks," in which he would meet each side in separate rooms - to set the ball rolling with only the Damascus delegation.
Under intense pressure, notably from the United States, the HNC later relented and arrived in Geneva on Saturday. However, the group questioned how long the delegation would stay.
"In view of the (Syrian) regime and its allies' insistence in violating the rights of the Syrian people, the presence of the HNC delegation in Geneva would not have any justification and the HNC could pull its negotiating team out," the group's coordinator, Riad Hijab, said in an online statement.
U.N. Secretary-General Ban Ki-moon described the talks - the first in two years - as long overdue. "I urge all parties to put the people of Syria at the heart of their discussions, and above partisan interests," he said on a visit to Ethiopia.
Opposition delegate Bassma Kodmani denied that her side was ready yet to negotiate. "We only came to Geneva after receiving assurances and commitments and we have precise commitments on the fact there would be serious progress on the humanitarian situation," she told a news conference. "We can't start political negotiations until we have those gestures."
The Syrian government's delegation head in Geneva, Bashar al-Jaafari, said the government was considering moves such as the creation of humanitarian corridors, ceasefires and prisoner releases, but suggested they might come about as a result of the talks, not before them.
"Absolutely, this is part of the agenda that we agreed upon and that will be one of the very important topics we will discuss among ourselves as Syrian citizens," Jaafari said.
Russian air strikes have killed nearly 1,400 civilians since Moscow started its aerial campaign in support of Assad nearly four months ago, the Syrian Observatory for Human Rights, a monitoring group, said on Saturday.
Kodmani said the bombings had increased in the last week. "In preparations for the negotiations everything has intensified. The sieges have become total," she added.
Islamic State claimed responsibility for Sunday's attacks in the Sayeda Zeinab district of Damascus, according to Amaq, a news agency that supports the militant group. It said two operations "hit the most important stronghold of Shi'ite militias in Damascus."
The Britain-based Observatory put the death toll at over 60, including 25 Shi'ite fighters.
Earlier the Interior Ministry had reported at least 45 dead and 110 people wounded, while state television showed footage of burning buildings and wrecked cars in the neighborhood.
The heavily populated area of southern Damascus is a site of pilgrimage for Shi'ites from Iran, Lebanon and other parts of the Muslim world.
The shrine houses the grave of the daughter of Ali ibn Abi Taleb, whom Shi'ites consider the rightful successor to Prophet Mohammad. The dispute over the succession led to the major Sunni-Shi'ite schism in Islam.
Islamic State has been excluded from the talks as the U.N. has classified it a terrorist group. Nevertheless Jaafari said the blasts confirmed the link between the opposition and terrorism, pointing to the attacks and comments from a leader of the Southern Front, another rebel coalition.
"This confirms what the Syrian government has said over and over again - that there is a link between terrorism and those who sponsor terrorism from one side and some political groups that pretend to be against terrorism," he said.
He said that the first way to help Syrians is to stop Turkey, Jordan and Saudi Arabia - which back the opposition - sending terrorists to the country. (Additional reporting by Suleiman al-Khalidi in Amman, Laila Bassam in Beirut and Michelle Nichols at the United Nations; Writing by David Stamp; Editing by Dominic Evans)