At least 35 soldiers were killed in twin suicide bombings and ensuing clashes with al Qaeda militants in Yemen on Sunday, hospital sources said, part of an upsurge in attacks since a presidential election two weeks ago.
A Yemeni army officer said at least 20 of the Islamist militants also died in the fighting in the country's south, an unstable territory near oil shipping routes through the Red Sea.
Residents and local officials said a vehicle exploded at a military position at the western entrance to the city of Zinjibar, near the Gulf of Aden. At least seven people were killed in that blast, medical sources said.
Another vehicle was detonated at an artillery position at the southern entrance to the city, killing and wounding an unknown number of people.
The Yemeni army sent reinforcements to Zinjibar from the nearby port city of Aden after the blasts.
Medics at a military hospital in the southern port city of Aden said the bodies of 35 soldiers had been brought in, and dozens more had been wounded. They said the number of casualties was likely to rise.
The attacks underscore the challenges facing newly elected President Abd-Rabbu Mansour Hadi as he tries to bring stability to Yemen after a year of protests against his predecessor, Ali Abdullah Saleh, that pushed Yemen to the brink of civil war.
Months of anti-Saleh protests weakened central government control over whole swathes of Yemen to the benefit of militants linked to al Qaeda which has expanded its foothold in the south.
A caller who said he was a spokesman for al Qaeda said the militant group was responsible for both attacks in which the two bombers died.
Zinjibar has been the site of regular clashes between the army and Islamist fighters who took the city for several months last year. The government said in September it had liberated Zinjibar from militant hands, but fighting has continued.
The heroes of the armed forces have dealt a painful blow to the al Qaeda elements in ... Abyan, the defence ministry said in a text message.
Residents of the militant stronghold of Jaar, about 15 km (10 miles) north of Zinjibar, said militants used megaphones to urge people to join the battle.
Last week an al Qaeda-linked militant group called Ansar al-Sharia said it would unleash a torrent of attacks unless the army pulled its forces away from Zinjibar within 10 days.
This is a clear escalation in al Qaeda operations in southern Yemen, which comes barely a week after the new president took office, said Radwan Mohammed, an analyst based in Aden.
A Yemeni government official said the attacks were part of a campaign to create confusion for the new president.
A U.S.-ally in the fight against al Qaeda, Yemen has allowed Washington to launch drone strikes on militants who regrouped there after successive blows suffered in Iraq and Saudi Arabia.
Wary of al Qaeda entrenchment in Yemen, the United States and Saudi Arabia backed a Gulf-brokered plan under which Saleh handed power to Hadi.
Yemenis said at least eight attacks had taken place since Hadi was sworn in last week, following the February 21 election.
The deadliest assault came hours after Hadi's inauguration when a suicide bombing killed at least 26 people at a presidential palace in eastern Yemen.
On Saturday, two suicide bombers drove a car packed with explosives into an army base in the southern province of al-Bayda, killing one soldier. A day earlier, a Yemeni Islamist group linked to al Qaeda attacked a U.S. security team in Aden.
(Additional reporting by Mohammed Ghobari in Sanaa; Writing by Sami Aboudi; Editing by Robin Pomeroy and Andrew Heavens)