Yemeni authorities sent more soldiers to the coastal town of Balhaf Saturday, a day after an alleged Al-Qaeda plot to attack a key gas terminal was foiled, a security official said.

The thwarted attack came after three other simultaneous assaults killed scores of security personnel in the lawless southern Al-Qaeda stronghold of Shabwa province, where Balhaf is also located.

Local and military officials have said 56 soldiers and policemen were killed in the three attacks.

State news agency Saba reported that 21 troops were confirmed dead and 15 wounded, but that the fate of "many" more was unknown.

"A 170-strong army force arrived at Balhaf" on the Gulf of Aden, the impoverished Arabian Peninsula country's only port for exporting liquified natural gas, the security official told AFP.

"On Sunday, the troops will be deployed at the checkpoints that were targeted in Friday's attacks and new checkpoints will be set up," the source said.

Friday's deadliest single attack was on an army camp responsible for ensuring security at Shabwa oilfields, the military said.

The two other attacks targeted an army checkpoint in Al-Nushaima area and a special forces camp at nearby Maifaa.

The defence ministry in Sanaa said a fourth Al-Qaeda attempt to detonate explosives targeting the Balhaf terminal ended in failure.

Security forces intercepted a vehicle which exploded, "killing the terrorists it was carrying," said the ministry's 26sep.net news website, without specifying how many militants died.

The authorities blamed Friday's bloodshed on Al-Qaeda in the Arabian Peninsula (AQAP), described by Washington, which strongly condemned Friday's attacks, as the jihadist network's deadliest franchise.

AQAP has not yet claimed responsibility for the attacks.

Witnesses told AFP Saturday that Yemeni jets flew over Balhaf and surrounding areas without carrying out any raids.

Last month, security was beefed up around Western embassies in Sanaa, and some were closed following warnings by Washington of an imminent attack.

President Abdrabuh Mansur Hadi said in August that a bid to attack the Balhaf terminal had been foiled after a phone call was intercepted between Al-Qaeda chief Ayman al-Zawahiri and AQAP leader Nasser al-Wuhayshi.

Sanaa also said it had foiled an Al-Qaeda plot to storm the Canadian-run Mina al-Dhaba oil terminal and seize the port of Al-Mukalla, capital of the eastern province of Hadramawt.

AQAP has denied plotting any such attacks.

Since succeeding Saleh, Hadi has repeatedly pledged to press the battle against Al-Qaeda in what is its slain leader Osama bin Laden's ancestral homeland.

Last month, Hadi said a wave of drone strikes on Al-Qaeda targets in August killed 40 militants in two weeks, including some ringleaders in the Sanaa region.

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