The United Nations and the Arab League on Thursday appointed former UN secretary-general Kofi Annan as their joint special envoy for the Syrian crisis, while Western and Arab nations prepare to meet in Tunis on Friday to discuss ways to further pressure the Syrian regime to end its 11-month-long crackdown on the opposition.

The UN said in a release that Annan will "facilitate a peaceful Syrian-led and inclusive political solution that meets the democratic aspirations of the Syrian people through a comprehensive political dialogue between the Syrian government and the whole spectrum of the Syrian opposition."

Around 70 nations and international organizations are set to meet Friday in Tunisia for the "Friends of Syria" conference. The Associated Press has reported that the Friends of Syria will issue an ultimatum calling for Syrian President Bashar al-Assad to implement a ceasefire and allow full humanitarian access to Syria or face further punitive measures, likely sanctions.

Russia and China, which voted against a UN Security Council resolution calling on Assad to step aside, will not be attending the conference.

US Secretary of State Hillary Clinton, meeting with foreign ministers and senior officials from around a dozen nations in London on Thursday, said that Beijing and Moscow may not be able to oppose action on Syria over the long run.

"The pressure will build on countries like Russia and China because world opinion is not going to stand idly by," Clinton said. "Arab opinion is not going to be satisfied watching two nations … bolstering a regime that is defying every rule of modern international norms."

'Breaking point'

The US secretary of state told reporters in London that there will be a "breaking point" in Syria, and the opposition will arm itself if the violence continues.

"There will be increasingly capable opposition forces," Clinton said. "They will from somewhere, somehow, find the means to defend themselves as well as begin offensive measures."

White House spokesman Jay Carney said that Washington still believes a "political resolution is the best approach" to the Syrian crisis and that arming the rebels "could lead down a dangerous path," but added that the Obama administration would "have to evaluate this as time goes on."

Crimes against humanity

International investigators on Thursday turned in a report to UN human rights chief Navi Pillay identifying senior Syrian military and political officials who they claim committed crimes against humanity.

The investigators said in their report that the Syrian government had "manifestly failed" to protect the Syrian people and security forces had systematically committed gross violations of human rights in "conditions of impunity." The report also documented instances of gross abuse by rebel fighters, many of them army defectors.

The Syrian government continued its bombardment of the flashpoint city of Homs for the 20th day on Thursday, despite international outrage over the deaths of 80 people, including two western journalists, on Wednesday.

The UN says over 5,400 people have been killed in Syria since the uprising began in March 2011. The London-based monitoring group Syrian Observatory for Human rights puts the number of dead at more than 7,600.

slk/ ipj (AP, AFP, Reuters, dpa)