US missions across the Middle East and Africa will be closed until Saturday after US intelligence uncovered what lawmakers said was the most serious threats of an al-Qaida attack in years.

The US State Department, saying it was acting "out of an abundance of caution", said 19 diplomatic outposts would be closed until the weekend.

Adding further tension to the situation, Interpol issued a security alert over the weekend after hundreds of militants were freed in jailbreaks.

The US list includes 15 embassies or consulates that were already closed on Sunday due to the security fears, as well as four additional posts. At least 25 US missions had initially been ordered closed.

On Sunday, US lawmakers said the move was prompted by electronic intercepts of high-ranking al-Qaida operatives signaling a major attack.

The intercepts were "probably one of the most specific and credible threats I've seen, perhaps, since Sept 11, 2001," said Michael McCaul, chairman of the House Homeland Security Committee.

An attack appeared to be imminent, possibly timed to coincide with the last night of Ramadan, McCaul told CBS.

'Lot of chatter'

Saxby Chambliss, vice- chairman of the US Senate Intelligence Committee, said there has been "an awful lot of chatter" among terrorists about planning an attack, all "very reminiscent of what we saw pre-Sept 11".

Chambliss, appearing on NBC's Meet the Press, said a US National Security Agency program that electronically intercepts mobile phone and e-mail communication helped gather intelligence about this threat.

The NSA programs have come under intense scrutiny since former intelligence analyst Edward Snowden leaked information to the media about the scope of the surveillance.

"If we did not have these programs then we simply wouldn't be able to listen in on the bad guys," said Chambliss, who described the information as "the most serious threat that I've seen in the last several years".

Dutch Ruppersberger, the top Democrat on the House Intelligence Committee, told ABC's This Week that US officials received information that high-level people from al-Qaida in the Arabian Peninsula were talking about a major attack.

Tight security

Security was especially tight in Yemen's capital Sanaa on Sunday where Britain, France and Germany shut their embassies.

Troops with armored personnel carriers were stationed outside the buildings as police and army checkpoints went up on all the city's main thoroughfares.

Residents said they heard the sound of a drone overhead, which could only be from the United States as Washington is the sole power to operate the unmanned aircraft in the region.

The US considers al-Qaida in the Arabian Peninsula to be the jihadist network's most active and dangerous branch, and has waged an intensifying drone war against the group's militants in Yemen.

Although Washington has responded to terrorist threats before by closing diplomatic missions, this is believed to be the most widespread closure.

Agence France-Presse