The military has claimed rapid victories against Al-Qaeda in southern Yemen but experts say the advances could be the result of a tactical retreat by militants in coordination with local tribes.
The army launched a major offensive on April 29 against the southern strongholds of Al-Qaeda in the Arabian Peninsula (AQAP), seen by Washington as the jihadist network's deadliest franchise.
President Abdrabuh Mansur Hadi said Wednesday that troops had "cleansed the provinces of Shabwa and Abyan" of militants.
Authorities say they have retaken several Al-Qaeda strongholds, including Huta, Azzan, and Rawda in Shabwa, and Mahfad and Ahwar in Abyan, after heavy fighting in which they say dozens of insurgents were killed.
"Al-Qaeda has lost the battle. It has lost important positions in the provinces of Abyan and Shabwa... now under army control," the military police commander in Shabwa, General Awad al-Awlaqi, told AFP.
The government has not provided a final toll for Al-Qaeda losses, and the army has since May 1 stopped providing figures on troop casualties.
And as troops closed in on AQAP strongholds in both provinces, the militants took refuge in surrounding mountain areas.
The governor of Baida province has warned that those elements as well as "sleeper cells in Baida might commit acts of vengeance".
The interior ministry had set up checkpoints around the provinces of Sanaa, Ibb, Baida, Lahij and Marib to keep out fleeing jihadists.
The authorities in Sanaa have also been on alert for revenge attacks and the US embassy has been closed to the public since May 7.
"The network has not lost its main strongholds in the south," a tribal source close to Al-Qaeda said, dismissing the government claims.
"What really happened was a tactical withdrawal of militants to regroup after they were dispersed under the pressure of the offensive," he told AFP.
The withdrawal was based on "agreements with tribal dignitaries," who adopt a "neutral" stance in an effort to protect their territories, the source said on condition of anonymity.
However, there is "widespread anger" among locals towards the militants, said the source.
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- 'Favourable environment' -
Troops on May 8 entered Azzan "without resistance" from Al-Qaeda fighters who withdrew to the nearby Al-Koor mountains, a local government official told AFP at the time.
The official spoke of "an agreement" reached between local tribes and Al-Qaeda, with militants pulling out without a fight "to spare the city bloodshed and destruction".
Days later, however, witnesses reported clashes between troops and militants in Azzan.
Zaid al-Salami, a Yemeni expert on Islamist groups, agreed that "the tribes offer Al-Qaeda a favourable environment."
"This was clear in Shabwa and Marib where tribes reached an agreement with the network to expel foreign insurgents while allowing members belonging to local tribes to stay," he said.
"This makes it difficult for the army to hunt down members of Al-Qaeda in tribal areas," he said.
Tribal loyalties run deep in the Arabian Peninsula country.
US-born Al-Qaeda cleric, Anwar al-Awlaqi, who hails from Shabwa, spent most of his time in a mountainous region controlled by his tribe, before a US air strike killed him in neighbouring Marib in September 2011.
AQAP took advantage of a 2011 uprising that forced veteran president Ali Abdullah Saleh from power to seize large swathes of the south and east.
The army recaptured several major towns in 2012 but has struggled to reassert control in rural areas despite recruiting militia allies among local tribes.
The latest offensive followed a wave of US drone strikes that killed scores of suspected jihadists in southern and central regions last month.
In the areas from which Al-Qaeda suspects fled, "we found trenches and underground hideouts built to shelter their leaderships from air raids," said a pro-army militia chief in Abyan, Abdullatif al-Sayed.
"The offensive will only succeed if these insurgents are hunted down wherever they hide," he said. Otherwise, "they will regroup to resume their operations".
Three weeks of air raids and clashes have sparked an exodus by local residents, with "more than 21,000" people displaced in Shabwa alone, according to activist Saeed al-Marnum.