Yemen's long-time ruler told tens of thousands of supporters today that he is ready to step down but cannot because he does not trust his opposition, whom he called "drug dealers".

Ali Abdullah Saleh spoke in a rare appearance before a cheering crowd outside his presidential palace in the Yemeni capital on a day of rival demonstrations.

Across town, an even larger number converged on a square chanting slogans calling for his removal and waving red cards emblazoned with the word "leave".

A week ago government security forces shot dead more than 40 demonstrators in Sanaa.

The bloodshed last Friday prompted a wave of defections by military commanders, ruling party members and others, swelling the ranks of the opposition and leaving the president isolated.

Saleh also imposed a state of emergency that allows media censorship, gives wide powers to censor mail, tap phone lines, search homes and arrest and detain suspects without judicial process.

The president, who has held power for more than three decades, has repeatedly sought to appease the protesters to no avail.

"We in leadership, we don't want power but we need to hand it over to trustful hands, not to sick, hateful, corrupt, collaborator hands," Saleh told his supporters, who carried pictures of the president and signs reading "No to terrorism!"

"We are ready to leave, but we want to do it properly and at the hands of our people who should choose their leaders," he said, calling the opposition a small minority of drug dealers, rebels and illegal money traders.

Security forces parked tanks and military vehicles close to the palace and beefed up their presence around Saleh's ruling party building and the interior ministry.

As he spoke, Saleh's forces tried to prevent more anti-government demonstrators from entering Sanaa.

Troops manning checkpoints on roads leading to the capital searched cars, trying to identify protesters, said a demonstrator who was turned away, Hamid al-Hawlani.

Protesters who had called for a million people to gather in Sanaa on Friday - the holiest day of the Muslim week, where believers traditionally congregate in mosques - also stepped up security around the central square where they have held demonstrations for weeks.

Pro-demonstrator forces patrolled the square clutching assault rifles and searching people trying to enter.