Armed tribesmen loyal to a powerful opposition leader Sadeq al-Ahmar seeking to oust Yemeni President Ali Abdullah Saleh have taken control of state news agency Saba in the capital Sanaa and were about to seize a nearby presidency palace on Wednesday, a security official told Xinhua.

The armed forces of Sheikh Sadiq al-Ahmar, chieftain of a powerful tribe coalition, seized the building of Saba news agency overnight after they killed one of the Republican Guards and wounded several others, the official said on condition of anonymity.

"They also seized the building of the culture ministry and tourism ministry. They are now besieging the nearby palace of President Saleh," he added.

He said the armed tribesmen were also trying to occupy the headquarters of the interior ministry and the ruling party in Hassaba district.

"The ministry of industry and trade, ministry of local administration and the National Airline Yemenia were all under control of the armed tribesmen of al-Ahmar, who stands by the opposition and supports protesters' demand to ease Saleh from power," the official said.

Fierce clashes have erupted in the capital Sanaa since Monday, hundreds of people from both sides have been killed or injured.