At least 30 people have been killed in Yemen during intense fighting between Sunni tribesmen and Shia Houthi fighters in the southern province of Bayda.
The gun battle erupted on Monday as the tribesmen, believed to be backed by al-Qaeda fighters, launched a counter attack to push back the Houthis who have been expanding their control of the city of Radaa, a predominantly Sunni area, Al Jazeera's Hashem Ahelbarra reported.
In recent weeks, the Houthis have launched operations against al-Qaeda fighters in the area, where US forces have also carried out drone attacks targeting top commanders of the armed group.
The latest violence comes a day after Yemen's new Prime Minister Khaled Bahhah and his cabinet were sworn into office, highlighting the challenge he faces in uniting the fractious country.
"This is a real test to the government," Al Jazeera's Ahelbarra said. "The real concern now in Yemen, if the fighting continues, is it's just going to deepen the sectarian divide, and lead to an explosive sectarian situation in the southern part of the country."
Our correspondent said the country's military is struggling to control the ongoing crisis, as their loyalties are also divided between the government and those who support the Houthis and former president Ali Abdullah Saleh.
Saleh is seen as the main backer of Houthi rebels who seized Sanaa in September unopposed, and have since expanded their control to coastal areas and regions south of the capital.
Some army troops that remain loyal to Saleh are accused of aiding the rebels.
Meanwhile, Houthi fighters signed a regional ceasefire agreement with tribal fighters supported by Ansar al-Sharia, an al-Qaeda affiliate, in al-Odain district in Ibb province of central Yemen, Al Jazeera's Khaled al-Hammadi, reporting from Sanaa, said.
Separately, Houthi rebel fighters kidnapped the head of Tihami movement, Abdulrahman Mokarram, in Hodeidah city in western Yemen on Monday.
The movement defends the rights of the Tihamah region in Yemen's west coast.
Yemen's ruling General People's Congress (GPC), whose many members are allied with former President Saleh, and the Houthi rebels have opposed the newly-formed government of Bahhah. The GPC said it was not consulted in the formation of the new cabinet.
Houthi rebels also rejected the new cabinet, demanding instead the dismissal of members they consider unqualified or corrupt.
On Saturday, the GPC's central committee dismissed President Abd-Rabbu Mansour Hadi from his posts as vice president and secretary-general of the party, accusing him of soliciting UN sanctions against Saleh.
Source: Al Jazeera