Fresh clashes broke out Sunday between Yemeni government forces and Shiite Huthi rebels, tribal sources said, ending an 11-day truce reached with mediation backed by United Nations envoy Jamal Benomar.
The renewed fighting in the northern province of Amran had shut off the road linking it to the capital, the souces said.
Clashes spread to the adjacent Sanaa province, where troops and rebels used heavy weapons in intense fighting in the Jarban and Jaess areas, according to the same sources.
It was not immediately possible to give a casualty toll, the sources said.
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Government officials and representatives of the Huthi rebels, also known as Ansarullah, reached a ceasefire deal on June 4 to end clashes in Amran province.
The agreement stipulated both sides would stop bringing military reinforcements to the area, impartial military monitors would be deployed, and the main road to the capital Sanaa reopened.
Huthis are suspected of trying to expand their sphere of influence as Yemen is split into six regions, pushing out from their mountain strongholds in the far north to areas closer to Sanaa.
The rebels complained Yemen would be divided into rich and poor regions under a federalisation plan agreed in February following national talks as part of a political transition.
Huthis have been fighting the central government for years, complaining of marginalisation under ex-president Ali Abdullah Saleh, who was ousted in a 2012 uprising.
In February, they seized areas of Amran province in fighting with tribes that killed more than 150 people.