SANAA (AFP) - Yemeni security forces fired tear gas and live rounds on Monday to break up a demonstration in Taez, south of the capital, killing three protesters and injuring dozens, witnesses and medics said. The security forces moved to disperse a sit-in which had overnight blocked the main road in Taez, witnesses said adding that troops fired tear gas and live rounds. A medical official said the dead body of a protester was taken to the local hospital while dozens of injured people were admitted. The dead man was identified as Mohammed Abdelhaq, 35. Witnesses and medics said two other demonstrators were later shot dead in further clashes, as the toll of people wounded by gunfire rose to 15, including three in serious condition. Thousands of teachers have been staging a sit-in outside the regional ministry of education offices in Taez, 250 kilometres (150 miles) south of Sanaa, demanding better pay and postponement of final exams, protest organisers said. Their action was joined by hundreds of anti-regime protesters who advanced from the city's "Freedom Square," where crowds had been staging a sit-in for the past several weeks. Demonstrators set up tents on the main Jamal road, where they spent the night, residents said. In the Red Sea city of Al-Hudaydah, 15 protesters taking part in a march in solidarity with Taez were injured, five of them by live rounds, witnesses said. A similar demonstration also staged in the town of Ibb, south of Sanaa, but no clashes were reported, witnesses said. Two other demonstrators were killed on Sunday when security forces intervened to disperse the protest after crowds besieged the local education ministry office and blocked the road, the state news agency Saba said. The official said seven policemen were wounded in the confrontation. On Saturday, security forces shot dead two students at a demonstration in Al-Maafar, in Taez province, demanding a postponement of exams as courses have been interrupted by strikes since anti-regime protests erupted in January. Taez, the second largest city in the impoverished Arabian peninsula country, has become a focal point for protests demanding the ouster of President Ali Abdullah Saleh, who has been in power since 1978. More than 150 people have been killed in the unrest, as Saleh stalls a Gulf-brokered deal which calls for his departure in 30 days after handing power to his deputy.