Suspected Al-Qaeda militants killed 18 Yemeni soldiers in separate ambushes Tuesday as the army launched a ground offensive against their remaining strongholds in the south, medical and security sources said.
Twelve militants were also killed when the ambush in Shabwa province sparked a firefight, tribal sources said.
Ten soldiers were also wounded and 15 captured, medics and an officer said.
The ground offensive, which was launched just hours before the opening of a donors' conference in London, seeks to capitalise on Al-Qaeda losses in a blistering US-backed air offensive last week in which nearly 60 suspected militants were killed.
That meeting brought a call from British Foreign Secretary William Hague for donors to back Yemen's efforts to give Al-Qaeda "nowhere to hide."
But the "Friends of Yemen" said the government must push through political and economic reforms if it wants donors to speed up payments of aid to the impoverished Arabian peninsula country
Commanders are seeking to expel the jihadists from a series of smaller towns and hill districts in Abyan and Shabwa provinces where they retained a presence after a 2012 offensive in which the army recaptured the major towns.
Al-Qaeda in the Arabian Peninsula -- a merger of the network's Yemeni and Saudi branches -- is regarded by Washington as its most dangerous franchise and has been subjected to an intensifying drone war this year.
The jihadists took advantage of a 2011 uprising that forced president Ali Abdullah Saleh from power to seize large swathes of the south and east, from which the army has struggled to evict them, despite backing from militia recruited among the local tribes.
Militants ambushed the army convoy near Al-Saeed, one of several towns in Shabwa province where troops backed by militiamen advanced overnight, an officer said.
Armed with machineguns and rocket-propelled grenades, they seized a troop carrier and captured 15 soldiers inside, and also destroyed three other vehicles, he added.
The army sent in "massive" reinforcements, another officer said.
Hours later, militants in Abyan province ambushed a convoy advancing towards Wadi Daiqa, where Al-Qaeda suspects were positioned, an officer there said.
They killed three soldiers and wounded seven, the source said.
Tuesday's incidents were a major setback to an operation launched amid great fanfare ahead of the Friends of Yemen meeting of governments keen to bolster security in the country, where Al-Qaeda attacks have spread even to the capital.
Defence Minister Mohammed Nasser Ahmed has travelled to the south to oversee the offensive, which "will not stop until these areas are purged of Al-Qaeda militants," an official said.
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- Security bolstered in capital -
In the capital, President Abdrabuh Mansur Hadi said extra "security measures" had been taken over fears of Al-Qaeda reprisals.
Just Monday, a German diplomat was wounded in an abortive kidnap attempt in the embassy district.
National Security chief Ali al-Ahmadi said the Supreme Security Committee had decided to "eradicate all forms of security problems" that had emerged during the uprising that forced Saleh out in 2012.
"This strategic aim shall not be abandoned until security and stability are restored," state media quoted him as telling a security meeting in Ataq.
Militia commander Hussein al-Wuhayshi said there was an "official decision to uproot Al-Qaeda from Abyan and Shabwa."
The ground offensive came after intense US and Yemeni air strikes on suspected Al-Qaeda targets last week that officials described as "unprecedented."
Air strikes on Abyan killed 55 suspected militants, while three more were killed in Shabwa.
A drone strike in Baida province further north killed 10 suspected militants and three civilians.
But DNA analysis of bodies recovered afterwards showed that no leading Al-Qaeda members were among the dead, a security official said.
AQAP leader Nassir al-Wuhayshi pledged in a rare video last month to attack Western "crusaders... everywhere in the world".
The video, which showed him addressing militants, could have been shot in the Al-Kur mountain range, which stretches between Abyan, Shabwa and Baida provinces, and is an AQAP stronghold, according to tribal sources.
Washington has kept up its drone war in Yemen despite mounting criticism of the civilian toll.
It says its use of the unmanned aircraft allows it to target jihadists without sending soldiers into lawless areas where local authorities have little or no control.