In a surprise move likely to turn pitched street battles into all-out civil war, Yemeni president Ali Abdullah Saleh returned to Sanaa late Thursday night.

Saleh, who had spent three months in Saudi Arabia recovering from wounds received during a June assassination attempt, had recently announced he would not return to Yemen and authorized his deputy to negotiate a transfer of power agreement.

The notoriously disingenuous Saleh has repeatedly promised to sign an agreement brokered by the six-member Gulf Cooperation Council, then refused at the last minute.

Saleh's absence had raised hopes he could finally be pressured into relinquishing power, but despite promises to the contrary, he has maintained a death grip on his 33-year rule.

Yemen destabilized during Saleh's absence, but the worst violence came this week when running battles with live fire and rockets erupted between Saleh loyalists and the troops of General Ali Moshen, who defected to the opposition earlier this year.

Reports say at least 100 protesters have been killed in this week's fighting, but it is unclear how many of the slain are armed opposition troops. Heavy clashes continued even after Saleh returned at dawn Friday.

For opposition leaders, Saleh's return means a bad situation will only get worse.

"His return means more divisions, more escalation and confrontations," Abdul Hadi Al Azizi told The Associated Press. "We are on a very critical escalation."

The United States and Saudi Arabia have been trying to dissuade Saleh from returning home in hopes of working out a peaceful transfer of power in a country where stability is vital to their campaign against Al-Qaeda.

Al-Qaeda-linked terror militias have already taken advantage of the unrest in Yemen and have seized control of several towns in the south.

Analysts say Saleh's return is likely to send the spiraling violence in Yemen into open civil war, which could shatter a nation with deep regional and tribal division.