The truce between the tribal groups and the forces loyal to President Ali Abdullah Saleh has been broken, bringing Yemen closer to a civil war, Reuters reported.
A government official said on Tuesday that the ceasefire agreement has ended.
The violence, between Saleh loyalist forces and Hashed tribesmen has been the bloodiest since the pro-democracy unrest erupted in January. The violence intensified when Saleh refused to sign a power-transfer deal, also know as the Gulf-deal.
The break of the ceasefire took effect after the two sides battled with machine guns, mortars and grenades, killing more than 115 in Sanaa.
Government troops and locals have been trying to force al Qaeda and Islamist militants from the southern city of Zinjibar after they seized the coastal town at the weekend.
Saba news agency reported on Tuesday that 21 Yemeni soldiers were killed on Monday in the clashes.
Opposition leaders have accused Saleh of deliberately allowing Zinjibar, a sea lane to fall in the hands of al Qaeda, where about 3 million barrels of oil passes daily, to show how chaotic Yemen would be without him.
At least 320 people have been killed in various clashes in Yemen since the protests started four months ago.
Under the Saleh regime Yemen has moved to the brink of a financial breakdown, with about 40 percent of the population living on less than 2 dollars a day.