A spokesman for the Joint Meetings Parties, a coalition of opposition parties, called the president “a liar” and said that the group had not been in communication with Mr. Saleh since a bloody assault on a demonstration last Friday that killed at least 50 people.

“He has one option and it is to leave now, right now, without delaying, without conditions,” the spokesman, Mohammed Qahtan, said…

A government official, who spoke in return for anonymity because he was not authorized to brief reporters, said on Tuesday that the details of Mr. Saleh’s proposal were not yet clear and were “still in the works.” The opposition plan, initially proposed by the formal opposition parties earlier this month but rejected by street protesters, urged Mr. Saleh to complete arrangements for his departure by the end of the year. But since then, the opposition parties have backed away from the offer, joining with street demonstrators calling for Mr. Saleh to quit immediately…

Military units appeared to take sides in the capital on Monday, with the Republican Guard protecting the palace of President Saleh and soldiers from the First Armored Division under the defecting military commander, General Ahmar, protecting the throngs of protesters in Sana.