And overnight, more than 400 people were hurt after police opened fire on a protest in the Red Sea town of Hudaida, doctors told the Reuters news agency.

Protesters have been urging President Ali Abdullah Saleh to resign.

Mr Saleh has said he is ready to discuss a "peaceful transition of power".

In office for more than three decades, he announced earlier this year that he would not seek another term in office in 2013.

Yemen, the Arab world's most impoverished nation, is one of about a dozen countries in the Middle East to have seen anti-government unrest this year.

In Taiz, a city of nearly half a million people 200km (125 miles) south of the capital Sanaa, witnesses told AFP news agency police had shot dead a young man who was tearing up a poster of the president on Sunday.

They continued to fire as security forces pushed back the demonstrators to a square where they had been holding a sit-in as part of nationwide protests.

One activist, Bushra al-Maqtari, told Reuters that tanks were being used.

"Armoured vehicles and tanks are surrounding us," she said. "They have spent three hours firing tear gas and bullets [in the air] in an effort to break up the protest."

Early on Monday morning, a demonstration was held in Hudaida, a city west of the capital, in protest at the crackdown by the authorities.

A few thousand people took part in the march, witnesses said.

"They suddenly gathered around the province's administrative building and headed to the presidential palace, but police stopped them by firing gunshots in the air and using tear gas," one witness said.

"I saw a lot of plain-clothes police attack them too," another resident said.

Doctors at a hospital in Hudaida said nine people were being treated for gunshot wounds, 350 were suffering the effects of tear gas inhalation, and 80 had been wounded by plain-clothes officers.

On Saturday, the opposition coalition Common Forum called on the president to hand over power to his deputy, Vice-President Abdu Rabu Hadi.

Common Forum, which includes the five biggest opposition groups in Yemen, offered a five-point plan for the handover:

• President Saleh resigns and is replaced by Mr Hadi

• Mr Hadi announces a restructuring of the security forces to make them accountable to the government

• An interim government is created based on national reconciliation

• A new electoral commission is established

• Civil liberties are boosted and an investigation is launched into the killing of protesters

Speaking at a meeting in Sanaa with representatives from Taiz Province on Sunday, President Saleh called on Common Forum to "end the crisis through calling off protests and removing roadblocks".

Any transition, he said, would have to be made "through constitutional ways".