At least 19 were killed in Yemen amid intense clashes that continued unabated despite President Ali Abdullah Saleh's most recent pledge to resign, medical officials said on Wednesday.

The deaths, both in the capital Sanaa and in the country's second largest city, Taez, came after Saleh told the US ambassador to Yemen on Tuesday that he would sign a Gulf-brokered power transition plan that calls on him to step down within 30 days.

Medical officials told Reuters the death toll from overnight violence reached 19, including a woman and her infant child who died in Taez when their house was struck by shells fired by government troops who, residents say, have been bombarding the city.

AFP reported that in the capital Sanaa, at least seven armed tribesman loyal to powerful Sheikh Sadeq al-Ahmar were killed in clashes overnight in the Hasaba district, the home of the chief and his extended family who have been battling government troops for weeks.

Yemen's government announced on its defense ministry website that nine soldiers fighting Sadeq's tribesmen and rival forces loyal to dissident General Ali Mohsen al-Ahmar were also killed overnight.

Mohsen and Sadeq, once Saleh loyalists, are now his mortal enemies, having thrown their support behind the protest movement as their troops battle Saleh's forces in increasingly deadly street clashes.

On Tuesday, the government declared a truce with Sadeq and Mohsen's forces, but according to Gulf News, gunfire and explosions were heard throughout the city within minutes of the announcement.

Saleh's opponents say his pledge to resign is meaningless due to his having backed out of similar pledges no fewer than five times since protests erupted in late January. Saleh, a dogged political survivor, has ruled Yemen for 33-years.

Yemen has witnessed one of the longest and bloodiest uprisings of the "Arab Spring" which, since January, that has left hundreds of Yemenis dead and thousands more wounded.