Yemen unrest: Troops fire on Taiz protesters
A BBC reporter says the situation in Taiz has escalated - this clip contains amatuer video purportedly taken in Taiz on Monday
Yemeni security forces have fired on anti-government protesters, killing at least 15 people and wounding many more, medical sources say.
Witnesses said snipers opened fire from the rooftops when protesters reached the governor's offices in Taiz.Snipers had also reportedly shot at protesters during a march in the fourth-largest city, Hudaida.
The unrest follows weeks of nationwide protests calling for President Ali Abdullah Saleh to stand down.
He has ruled the country for 32 years, and has signalled that he has no plans to leave immediately.
Live ammunition On Monday, crowds of protesters in the south-western city of Taiz began marching toward Freedom Square - the focal point of protests, where demonstrators have been camping out.
When the march passed the governor's headquarters, troops blocked the procession and clashes broke out.
Continue reading the main story 
Yemen's leader has been one of Washington's key allies in the war on terror. Yemen is home to one of al-Qaeda's most dangerous franchises. The inability of the government in Sanaa to control much of its territory gives al-Qaeda in the Arabian Peninsula space to train and grow.
Yemen occupies a piece of strategic real-estate near to the mouth of the Red Sea. Yemen as a totally failed state, dominating a key shipping route to and from the Suez Canal, is a nightmare for Washington; a kind of Afghanistan-on-sea before the ousting of the Taliban.
The growing violence and President Saleh's refusal to give up power has prompted something of a shift in the US view over the past couple of weeks. Mr Saleh is now seen by the Obama administration as less of an asset and more of a liability.
Analysis
Yemen occupies a piece of strategic real-estate near to the mouth of the Red Sea. Yemen as a totally failed state, dominating a key shipping route to and from the Suez Canal, is a nightmare for Washington; a kind of Afghanistan-on-sea before the ousting of the Taliban.
The growing violence and President Saleh's refusal to give up power has prompted something of a shift in the US view over the past couple of weeks. Mr Saleh is now seen by the Obama administration as less of an asset and more of a liability.
Activists described chaotic scenes, with live ammunition being fired and military police taking away the bodies of dead protesters.
"It was heavy gunfire from all directions. Some were firing from the rooftop of the governor's building," a witness told the Associated Press.Hospital sources said at least 15 people had been killed, and 30 more were wounded.
Tanks and armoured vehicles are now blocking entrances to the city and have surrounded Freedom Square, arresting anyone who tries to leave.
The port city of Hudaida saw demonstrators gather in solidarity with people in Taiz and attempt to march on the city's presidential palace.
But police opened fire on them with live ammunition and tear gas leaving dozens injured, witnesses and doctors 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. I saw a lot of plain-clothes police attack them too," an unnamed witness told Reuters news agency.
Collapsing economy
A BBC correspondent in the country, who cannot be named for security reasons, says President Saleh is under immense pressure.
He has lost allies, the army is split, the government has lost control of entire areas of the country and the economy is collapsing, says our correspondent.
- President Saleh resigns and is replaced by Vice-President Abdu Rabu 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
Any transition, he said, would have to be made "through constitutional ways".
Are you in Taiz? Have you witnessed the violence? Send us your comments using the form below.
