Qatar on Thursday pulled out of a Gulf-brokered plan to ease Yemen's president Ali Abdullah Saleh from power, Gulf News reports.
Qatar's withdrawal came as the the Gulf Cooperation Council (GCC), of which it is a member, was sending its secretary-general, Abdul Latif Al Zayani , to Yemen to revive the stalled deal.
Zayani, who is expected in Sana'a on Saturday for  a new attempt to revive the flagging initiative, condemed the renewed violence in Yemen.
"I call on all sides to return to the Gulf initiative to solve the crisis, as it is the best exit to the tragic situation Yemen is living," he said in a statement.
The accord has been teetering on the brink of collapse for weeks as Saleh, a shrewd political survivor in power for 33 years, refused to sign the deal.
The plan, mainly backed by regional heavyweight Saudi Arabia, was intended to stop weeks of bloodshed, but the withdrawal of Qatar, which has mediated in several conflicts in the Middle East and Africa, is a stark psychological blow.
"Qatar was forced to take this action because of the stalling in signing the proposed agreement ...the continued escalation, the intensity of the confrontations and a lack of wisdom," the Qatari state news agency QNA reported, citing a Foreign Ministry official.
Saleh has accused Qatar of funding the opposition in Yemen and said the gas-rich Gulf state's pan-Arab television channel Al Jazeera has provoked the protests.
Yemeni forces fired machine guns to halt a protest against Saleh on Thursday, wounding dozens in the southern city of Taiz and two protesters were killed in another southern city.
Jet fighters were used to strike anti-Saleh tribesmen in Yemen this week as well.
Immunity Clause Challenged
US-based Human Rights Watch called for Saleh's immunity under the GCC deal to be withdrawn after the latest attacks on protesters.
"These attacks suggest that President Saleh views his promise of immunity as a `Get Out of Jail Free' card for political murder," the group said in a statement.
"The GCC member states and other governments involved in negotiations for President Saleh's exit should immediately pull immunity from the table," the statement read.
This week's bloodshed may fuel public rage before Friday, the Muslim day of prayer and traditionally the largest day of rallies in the three-month-old revolt against Saleh.
"The more the regime thinks it's reaching its end, the more it increases the violence against us, but we'll remain firm and we're not leaving," Sana'a protester Abdul Karim Mohammad told reporters
The defence ministry said Thursday Saleh planned to deploy military academy students to help security forces.
That may indicate he is running out of manpower after recent political, tribal and military defections.
Protesters are increasing pressure by trying to blockade government buildings as they grow increasingly frustrated by their inability to dislodge Saleh.
Anti-Saleh tribesmen have blockaded the oil-producing Maarib province for weeks, creating a fuel crisis shipping sources say is costing Yemen $3 million a day in blocked exports.
Join our official WhatsApp group