SANAA (AFP) - A truce reached by Yemens government and dissidents, who have been locked in bloody battles for weeks, collapsed as soon as it was announced on Tuesday with fresh fighting rocking the capital. Fifteen people were killed in Sanaa and Taez, most of them in Yemens second largest city, medical and tribal sources said. Medics said at least seven people were killed in Taez, including a seven-year-old child, a woman and a policeman, during what residents said was random shelling by government forces of neighbourhoods. The interior ministry said four policemen also died. In Sanaa, the truce failed to take hold. Tribal sources said at least one man was killed and nine people were wounded when shelling rocked the northern Al-Hasaba neighbourhood. The govt and dissident general Ali Mohsen al-Ahmar had reached a ceasefire agreement, according to an official statement. Tribal forces in Al-Hasaba led by powerful chief Sheikh Sadiq al-Ahmar, who backs the general and has thrown his support behind pro-democracy protests across Yemen, also agreed to the ceasefire, sources in his office told AFP. The govt statement said the truce went into immediate effect, but Sadiqs brother, Sheikh Hemyar, told AFP that President Ali Abdullah Salehs troops continued to attack the Ahmars homes. The truce was not respected for one second by the government, Sheikh Hemyar told AFP by telephone. As I talk to you, our homes are being shelled in the district of Al-Hasaba. Residents in Al-Hasaba confirmed that the area was being raked by gunfire and explosions. Meanwhile, President Ali Abdullah Saleh told the US ambassador in Sanaa that he is committed to a plan to step down amid political violence, the State Department said. State Department spokeswoman Victoria Nuland welcomed Salehs remarks but said that he needed to live up to his promises, after a string of statements by the veteran leader voicing support for the plan without implementing it. Saleh met with US Ambassador Gerald Feierstein to discuss developments in Yemen after the UN Security Council and the US both urged him to begin the transfer of power immediately, Nuland said. It is a positive step that he called the ambassador in and recommitted to him to us, to the international community that he intends to sign it, Nuland told reporters. So now we look for him to make good on that commitment, she said. Gunfire also rang out near Change Square, the epicentre of anti-regime protests outside Sanaa University, where the dissident generals troops have been deployed since March, local residents said. Tuesdays announcement came just hours after Salehs troops opened fire on thousands of pro-democracy demonstrators in the capital killing three people and wounding at least 40 others. A government crackdown on unarmed protesters in Sanaa has left hundreds dead and thousands wounded since January. This is the third ceasefire breached since May between the government and tribal chief Sadiq, whose well-armed tribesman have been engaged in fierce battles with Salehs troops in the capitals Hasaba district.