Mr Saleh has appeared to be ready to resign several times, but pulled out of deals to stand down at the last moment.

He returned to Yemen unexpectedly last month from Saudi Arabia where he had been receiving treatment after his office was shelled in June. He is faced with protests and an insurrection by renegade army units.

He has also repeatedly refused to sign a transition deal brokered by Gulf states, and first presented in March, whereby he would hand over power to his vice-president in return for immunity from prosecution.

In Mr Saleh's speech, broadcast on state television, he gave no precise date for standing down.

In his first interview since returning to Yemen in late September, Mr Saleh said he would not stand down as promised if his opponents were allowed to stand in elections to succeed him.

Anti-government protesters have been camped out in an area of the capital Sanaa - dubbed Change Square - since January, demanding an end to President Saleh's rule.

Yemen is facing multiple security challenges, including fighting between political factions and an al-Qaeda militancy in the south.