GENEVA -- Syria peace talks ran into trouble on Monday, with the UN mediator saying the opposition has suspended its formal participation in the indirect discussions with President Bashar Assad's government to protest "worrisome" new violence, especially near the northern city of Aleppo, and rising concerns about the humanitarian situation.
Staffan de Mistura, the U.N envoy for Syria, said he will press on with the talks despite the suspension by the opposition High Negotiations Committee. The HNC said it would no longer attend meetings at the UN office in Geneva that has hosted weeks of on-and-off peace talks aimed ultimately at ending the country's devastating five-year war.
The HNC delegation will remain at their hotel in Geneva, and de Mistura said he will continue "technical" discussions with its envoys by phone or off-site in hopes of firming up a blueprint for a political transition in Syria. He said he would "take stock" of progress toward that goal on Friday.
De Mistura has repeatedly said that political transition -- as called for under a UN Security Council resolution -- is "the mother of all issues." On Monday, he acknowledged a "gap" between the two sides on that issue: the HNC wants no role for Assad in any transitional government, and Assad's envoys have proposed a "broad-based government."
"Both of them (are) claiming this is the road to political transition," he said, adding that the two sides agreed on the need for such a transition, but had differences of "interpretation" about what that meant.
The suspension came just hours after Syrian opposition fighters launched a new offensive against government forces in a number of northwestern areas. Rebel groups said attacks in rural parts of Latakia province, a government stronghold, were in retaliation for violations of a U.S. and Russian-brokered cease-fire.
De Mistura said the new fighting in parts of Syria, especially near Aleppo, was "particularly worrisome," and said that he expected that the U.S. and Russia -- who are leading oversight of the truce -- will hold a special meeting about it "if this trend continues."
In a statement, the Kremlin said Russian President Vladimir Putin and U.S. President Barack Obama discussed the situation in Syria and agreed to increase co-ordination between the special services and militaries of the two countries.
The HNC's chief negotiator, Mohammed Alloush, said the fragile cease-fire that started in late February "has effectively been ended by the regime." He said government forces carried out 70 air raids on Sunday, Iran had sent in two new fighting groups to help reinforce Assad's troops, and Russia has supplied Syrian soldiers with weaponry.
"All this intervention gives a clear indication that the solution in Syria, with the presence of this regime, has become shut -- or we have hit a wall," he told The Associated Press.
The rebels said the offensive came in response to government attacks against refugee camps and residential areas. Different rebel factions shared videos of their fighters lobbing rockets at government positions in the Jabal al-Akrad area, close to the rebel-held northwestern province of Idlib. They claimed on social media to have gained ground.
The Britain-based Syrian Observatory for Human Rights confirmed the rebels seized control of at least two areas and said al Qaeda's branch in Syria, the Nusra Front, is taking part in the fighting. Neither the Nusra Front nor the Islamic State group is included in the cease-fire.
The cease-fire, which has been planned to help buttress the Geneva talks, had reduced violence across Syria despite alleged violations on both sides. The opposition says the government has breached the agreement more than 2,000 times. De Mistura has said that many Syrian civilians have felt positive effects from the truce overall.
The truce has held in most of Syria, except in the north, where it has practically collapsed. The Nusra Front is deeply rooted in the areas in northern Syria controlled by opposition forces, complicating the oversight of the truce.
A Syrian opposition member in Geneva, Mohammed al-Abboud, said the rebels have the right to defend themselves.
"We have the right to retaliate and defend ourselves in case we are attacked and we will not be silent about any aggression and we will continue our main mission to defend civilians," al-Abboud said in comments published on the Syrian opposition High Negotiation Committee's Twitter account.
Syria's UN ambassador Bashar Ja'afari, who is leading the government's delegation in Geneva, accused rebel fighters of calling for a "revocation of the cessation of hostilities." Before de Mistura spoke, Ja'afari said that the government delegation planned to meet with him again on Wednesday.
In Moscow earlier Monday, Russian Foreign Minister Sergey Lavrov said the two sides in Geneva should move to direct talks. The two delegations only have met separately with de Mistura, not face-to-face. Lavrov also denied claims that Moscow and Washington were negotiating Assad's departure behind closed doors.
