Attackers have stabbed a Yemeni provincial governor and at least 60 other people were injured in confrontations around the nation between security troops and protesters seeking to topple the country's leader of 32 years.
A month of protests set in motion by the tumult sweeping the Arab world is spiralling out of control in Yemen, already one of the most impoverished and volatile corners of the Middle East.
President Ali Abdullah Saleh - who has faced down threats from an al-Qaida offshoot, a secessionist movement in the south and a seven-year armed rebellion in the north - has been unable to stop street protests that are unprecedented in their scope and in the broad cross-section of society taking part.
In a sign of his frustration, President Saleh fired the government minister in charge of trying to engage his opponents in dialogue.
In the eastern Marib province, a predominantly tribal area, protesters staged a large demonstration outside the local government building and shouted anti-regime slogans.
Security troops fired live ammunition and tear gas, injuring around 37 people. In the melee, a group of men stabbed Governor Naji al-Zaidi and four bodyguards with daggers, the Interior Ministry said.
In the southern city of Taiz, police tried to disperse demonstrators with gunfire and tear gas, injuring three people. Clashes in the north-eastern province of Jawf injured at least 20 more.
The unrest in Yemen is of deep concern to the United States and other world powers, in particular because al-Qaida has established one of its most dangerous offshoots in the country's mountainous hinterlands.
It has launched attacks beyond Yemen's borders, including a failed attempt to blow up a US-bound plane in December 2009 with an explosive device sewn into the underwear of a would-be suicide bomber.