Yemeni security forces were on high alert Saturday for more Al-Qaeda reprisals over an offensive against them, after militants killed five presidential guards and ambushed the defence minister's convoy.
The interior ministry said security forces in Sanaa had been reinforced, particularly around government installations and embassies.
It added that new checkpoints had been set up around the city to "block all terrorist acts" and that security forces were working "around the clock... to preserve security in the capital."
There were also fears that reprisals might be carried out in the central province of Baida, one of three where the army has been pursuing a campaign against jihadists since April 29.
On Friday, suspected Al-Qaeda militants attacked the presidential palace in Sanaa, killing five guards and triggering a fierce gunfight as they hit back at the offensive aimed at crushing them.
President Abdrabuh Mansur Hadi was not at the palace when gunmen attacked a checkpoint manned by guards outside the compound, a security source told AFP.
Hadi, whose government has stepped up a war on Al-Qaeda in the Arabian Peninsula -- a merger between the network's Saudi and Yemeni branches -- uses the palace only for meetings.
Sanaa has been on alert for days, and tensions rose after the army said troops had entered Azzan, a jihadist bastion in southern Shabwa province, prompting the United States to close its Sanaa embassy on Thursday.
That night security forces killed Al-Qaeda commander Shayef Mohammed Said al-Shabwani, one of the network's most wanted leaders suspected of masterminding the abduction of Western diplomats, in a gunfight near the presidential palace.
On Friday, Defence Minister Mohamed Nasser Ahmad and two senior security officers escaped unharmed when gunmen ambushed their convoy as they returned from a tour of the south .
Ahmad has vowed to crush Al-Qaeda fighters in Yemen and on Friday told troops in Shabwa and Abyan that the offensive will continue until "the last criminal and evil" militant is killed.
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The army launched its offensive on April 29 against AQAP strongholds in the contiguous provinces of Shabwa, Abyan and Baida, and claims it has inflicted heavy losses on the jihadists.
AQAP is regarded by Washington as Al-Qaeda's most dangerous franchise and has been linked to failed terror plots in the United States.
- 'Slepper cells' -
On Monday, the interior ministry warned that "huge losses" in jihadist ranks "will push Al-Qaeda to commit hysterical and desperate acts."
Officials said Saturday morning that the situation was relatively calm in Shabwa and Abyan, but state news agency Saba reported without giving details that "seven terrorists" had been killed in the two provinces.
Meanwhile, a tribal source said that, as government forces close in on their strongholds in Shabwa and Abyan, Al-Qaeda fighters had taken refuge in Al-Kur, a mountainous area linking them and Baida.
On Friday night, Baida Governor Ahmed al-Shaddadi issued a statement in which he did not rule out that those elements, as well as "sleeper cells in Baida might commit acts of vengeance."
He urged residents to cooperate with security forces and "denounce all suspect movements by... those who had fled fighting in Abyan and Shabwa."
AQAP leader Nasser al-Wuhayshi vowed, in a rare video appearance posted online in April, to attack Western "crusaders" wherever they are.
Al-Qaeda uses the term crusaders to refer to Western powers, especially those which have intervened militarily in Muslim countries, such as Britain, France and the United States.
The jihadists took advantage of an Arab Spring-inspired uprising that forced autocratic president Ali Abdullah Saleh from power to seize large swathes of southern and eastern Yemen.
The army recaptured several major towns in 2012 but has struggled to reassert control in rural areas, despite the backing of militiamen recruited from tribes.