New US drone strikes reportedly killed seven alleged al-Qaida members in southern Yemen on Wednesday after the government in Sana'a claimed to have foiled a large-scale terrorist attack and the US and Britain evacuated their embassy staff.

Security officials told the Associated Press the latest drone attacks hit targets in Shabwa province, where residents reported seeing two vehicles and several bodies on fire.

The news came as details emerged in the capital of an ambitious plan by al-Qaida in the Arabian Peninsula (AQAP), a "franchise" of the global terrorist network, to attack oil installations and towns.

Rajeh Badi, press adviser to Prime Minister Mohammed Salem Basindwa, said the plot involved dozens of fighters in Yemeni army uniforms storming the facilities on Sunday night, and holding them. Yemeni officials spoke of a plan to take control of the Mina al-Dhaba oil terminal, which is run by Canada, in the Mukallah region on the Arabian Sea.

The US state department said on Tuesday that its decision to close its embassy and to repeat a call for all US citizens to leave the country had been prompted by a "specific and immediate threat."

US intelligence is reported to have earlier intercepted "chatter" indicating an impending terrorist attack, along with a conversation between the al-Qaida leader Ayman al-Zawahiri, who is believed to be in hiding in Pakistan, and Nasser al-Wuhayshi, the head of AQAP.

The New York Times said the conversation represented one of the most serious plots since the 9/11 attacks prompting the closure of 19 US embassies worldwide. Britain and several other western countries followed suit. "This was significant because it was the big guys talking, and talking about very specific timing for an attack or attacks," the New York Times quoted one official as saying.

Yemeni officials told AP they believe the motive for the planned attacks was retaliation for the killing of Wuhayshi's deputy, Said al-Shihri, who was critically wounded in a November drone strike and later died of his injuries.

The US response to the threat has triggered renewed criticism of the Obama adminstration's approach to Yemen, which is said to include tactics tried in Pakistan and Afghanistan but which are inappropriate to conditions in the Arab world's poorest and intensely tribal country.

"US efforts to decapitate the leadership of al-Qaida in the Arabian peninsula have resulted in the deaths of many civilians, yet there is no certainty as to who the targets really are," commented Christina Hellmich of Reading University. "The membership of AQAP remains unknown while the deaths worsen the problems for the US in the region, by supporting the political legitimacy of the jihadis as they struggle to establish a position in the contested state."

AQAP has attempted to mount several attacks on US soil, including a bid to bring down a passenger plane over Detroit in 2009 by a man wearing explosives in his underwear, and a failed plot to send bombs concealed in printers.

Earlier that year the group tried to assassinate the Saudi security chief, Prince Muhammad bin Nayef, with a bomb that was concealed on the attacker's body.

The Sana'a government said this week that it was hunting 25 named AQAP operatives it suspects of planning attacks.