In the biggest demonstration against the President yet, many thousands of Yemenis have gathered in capitol city of Sanaa demanding the immediate resignation of Ali Abdullah Saleh.

The atmosphere is reportedly very tense, a week after more than four dozen demonstrators were killed by security forces. (Saleh has denied that government troops participated in the wanton killing of protesters). Both the government and opposition groups have established check points in the city and the streets are crowded with armed men.

A correspondent for Al Jazeera in Sanaa said: People here are concerned and fear a repeat of last Friday's violence. There are two or three makeshift medical centers set up around the square, and people are trying to get as many medical supplies into them as possible. In the past seven days, a lot of momentum has gathered behind these protesters. And if people do make the journey from here to the presidential palace, that will certainly be a flashpoint - and further violence, is likely.”

Saleh, in power since 1978 and a strong U.S. ally, has reportedly offered to step down, but only to capable, responsible hands.

He is facing immense pressure and increased isolation after several of his top military aides defected to the opposition. The most prominent defection was by a senior general, Ali Mohsen al-Ahmar, once the second most powerful man in the country. Mohsen as reportedly sent his own troops to protect demonstrators in Sanaa.

Saleh called their decision to leave “stupid” and has offered amnesty if they return to the fold.

The opposition has already rejected his calls for early elections. Nothing will satisfy them except Saleh’s prompt exit.

No dialogue and no initiatives for this dead regime, opposition spokesman Mohammed al-Sabry said on Thursday.

Protesters are also seeking a new constitution and the elimination of parliament, local councils and the notorious state security forces.

On Wednesday, Yemen’s parliament enacted temporary emergency laws that give state security units extraordinary powers to arrest and hold suspects.

Saleh has repeatedly warned that without him Yemen would sink into the chaos of a civil war, given the existence of a separatist movement in the south, as well as the presence of Al Qaeda terrorist guerillas in the hinterlands.

However, there are now reports that Mohsen and Saleh have privately met to discuss terms of Saleh’s departure.

Mohsen claims he does not want to rule the country.

Ali Mohsen as an individual has served for 55 years and has no desire for any power or position, he told Reuters.

I have no more ambition left except to spend the remainder of my life in tranquility, peace and relaxation far from the problems of politics and the demands of the job.

Meanwhile, the US and UK have urged their nationals to either leave Yemen or avoid the protests.