Syria's foreign minister has accused America of trying to create a "negative climate" at the second round of peace talks as US secretary of state John Kerry blamed "the Assad regime's obstruction" for making the tense dialogue even more difficult.
Walid al-Moallem spoke out a day after the meetings in Geneva, Switzerland, between Syrian president Bashar Assad's government and the opposition seeking his removal ended without finding a way of breaking the impasse in the nearly three-year-old conflict.
Mr al-Moallem told the state news service that the US tried to "create a very negative climate for dialogue in Geneva".
For his part Mr Kerry repeated the US commitment to finding a political solution to the civil war and praised the opposition's "mature seriousness of purpose and willingness to discuss all aspects of the conflict".
But he said: "While it stalled in Geneva, the regime intensified its barbaric assault on its civilian population with barrel bombs and starvation. It has even gone as far as to add some of the opposition delegates at Geneva to a terrorist list and seize their assets. This is reprehensible."
Syria's conflict started as largely peaceful protests against Assad in March 2011 but later degenerated into a civil war in which more than 140,000 people have been killed, according to activists.
The United Nations' human rights office said in January it had stopped updating the death toll from the war, confirming that it could no longer verify the sources of information that led to its last count of at least 100,000 in late July.
Millions have been driven out of their homes, seeking shelter in neighbouring countries and in safer parts of their homeland.
Washington, its European and Persian Gulf allies are backing the opposition in Syria's conflict. Russia and Iran support Assad's government.
UN-Arab League mediator Lakhdar Brahimi apologised to the Syrian people yesterday for failing to reach progress.
"I am very, very sorry, and I apologise to the Syrian people that their hopes which were very, very high that something will happen here," he said.
More than 5,792 people have reportedly have been killed in Syria since the Geneva talks began on January 22, activists said.
The talks' modest achievement has been a UN-brokered truce in the central city of Homs that has allowed aid workers to deliver some food and medicine for hundreds trapped in the rebel-held areas. More than 1,000 people were also evacuated from the city, which has been under government blockade for more than a year.
Yesterday the Syrian Arab Red Crescent said its workers entered the western Damascus suburb of Moadamiyeh to deliver food for the first time in 15 months of government blockade.
Head of operations Khaled Erksoussi said the agency was allowed to take 500 food parcels into the suburb. A truce has been in place in the area for two months, but Moadamiyah remains surrounded by army checkpoints and troops, he said.
He appealed for more aid to be allowed for at least 10,000 residents of the suburb that was attacked by chemical weapons in August.
The leader of Lebanese militant group Hezbollah, Sheikh Hassan Nasrallah, pledged to fight on alongside Assad's troops until Sunni Muslim extremists fighting with the rebels were defeated.
"We will remain where we should be, our policy hasn't changed," he said in a televised speech to commemorate the death of three of the group's leaders, including top military commander Imad Mughniyeh who was killed in a Damascus car bombing in 2008.
Hezbollah fighters have been key to the Syrian army's success on the battlefield since June, when they helped Assad's forces dislodge rebels from the opposition stronghold of Qusair near the border with Lebanon.