The UN named its former leader Kofi Annan as special envoy for Syria on the eve of an international conference on Friday aimed at pressuring the Assad regime to halt the rising spiral of violence.
Amid international outrage over the deaths of two Western journalists and reports of intensified shelling of civilians, Annan was called on to represent both the UN and the Arab League in ending "violence and human rights violations, and promoting a peaceful solution to the Syrian crisis," the two bodies said in a statement on Thursday.
The appointment came on the day international investigators submitted a list of Syrian military and political officials suspected of possible crimes while the death toll continued to mount inside the country.
More than 7,500 people have been killed in 11 months of protests against President Bashar al-Assad and there is growing international pressure for an initiative seeking to end the murderous government crackdown.
Western and Arab powers are to push Syria to allow in desperately needed humanitarian aid at an international conference in Tunis Friday.
More than 60 nations are gathering for the crucial Friends of Syria conference, which will also seek to further isolate Assad's regime and support the country's opposition.
But the Arab League-organised conference of Arab and Western officials, including US secretary of state Hillary Clinton, will be marked by a Russian boycott and the absence of China.
Both countries have frustrated efforts to rein in Assad's regime, including by vetoing UN Security Council resolutions.
An early draft of the meeting's declaration being circulated by opposition sources Thursday said it could call for the Syrian government "to implement an immediate ceasefire and to allow free and unimpeded access by the UN... and humanitarian agencies."
"We look forward to concrete progress on three fronts: providing humanitarian relief, increasing pressure on the regime, and preparing for a democratic transition," Clinton told reporters in London on the eve of the talks.
"To that end, we hope to see new pledges of emergency assistance for Syrians caught in Assad's stranglehold, and international coordination and diplomatic pressure on Damascus to allow it to get to those who need it most."
As President Assad's regime brushed off outrage over the deaths of two Western journalists in Homs, activists spoke of "terrifying explosions" while his forces pounded the city for a 20th straight day.
The White House slammed the attacks as "heinous and unforgivable," as monitors said 86 people were killed across Syria on Thursday, 61 of them civilians.
"That's why we're working with a broad array of international partners to isolate and pressure Assad, to bring around a peaceful transition in that country, a transition that is inevitable and already under way," President Barack Obama's spokesman Jay Carney said.
"We continue to believe that a political resolution is the best approach," he added, noting that arming rebels or other military involvement could "lead down a dangerous and chaotic path," though Washington would "have to evaluate this as time goes on."
The latest bombardment of Homs -- Syria's third-largest city -- centred on Baba Amr neighbourhood, where US reporter Marie Colvin and French photojournalist Remi Ochlik were killed on Wednesday.
"Baba Amr, as well as parts of Inshaat, have been shelled since 7:00am (0500 GMT), while mortar rounds slammed into the Khaldiyeh neighbourhood," said Rami Abdel Rahman of the Syrian Observatory for Human Rights.
Activist Hadi Abdullah told AFP from inside the city: "We hear terrifying explosions."
He said the world outcry over the deaths of the journalists and 24 Syrian civilians in Homs on Wednesday appeared only to have strengthened the regime's determination to eliminate all opposition in the city.
"The more the condemnations pile on, the heavier the bombing becomes," Abdullah said.
In Geneva, international investigators said they had submitted a list of Syrian military and political officials suspected of possible "crimes against humanity" to UN human rights chief Navi Pillay.
The UN-commissioned panel said it documented a widespread and systematic pattern of gross violations by Syrian forces, "in conditions of impunity," since March 2011 when the popular uprising against Assad's regime broke out.
It said Syria's government had "manifestly failed" to protect its people, but also said it had found instances of gross abuses committed by rebel fighters, many of them army defectors.
Abdullah said there was evidence regime forces deliberately targeted the makeshift media centre where Colvin and Ochlik were killed and two others wounded.
"We are sure that the centre was targeted, because 11 rockets struck in and around it," he said. "The regime forces intercepted a transmission signal."
The Syrian government made no denial its forces had fired the lethal rounds.
"We reject statements holding Syria responsible for the deaths of journalists who sneaked into its territory at their own risk," said the foreign ministry.
Efforts were under way to evacuate the two wounded journalists -- Edith Bouvier, a reporter for French daily Le Figaro, and Sunday Times photographer Paul Conroy.
Britain said on Thursday Conroy was "on his way out" of the besieged city, while Bouvier appeared in a video posted online asking to be evacuated quickly, saying she needed urgent medical attention.
Iran's supreme leader Ayatollah Ali Khamenei said Assad's regime will not fall and that Tehran "supports the Syrian government and will oppose those who act against Syria."