The United States has temporarily closed 21 embassies and consulates in mostly Muslim countries, and several European states have shut embassies in Yemen over fears al-Qaeda was planning to launch attacks.
The US closed its facilities on Sunday, after saying it had information that al-Qaeda and its allies may increase efforts to attack Western interests this month.
The closures came as Interpol issued a global security alert after hundreds of inmates were set free in prison breaks linked to al-Qaeda, and suicide bombers killed nine near the Indian consulate in the Afghan city of Jalalabad.
Lawmakers briefed on the intelligence called the threat reporting among the most serious they had seen in recent years. General Martin Dempsey, the chairman of the US joint chiefs of staff, said the specific locations and targets were not known, but "the intent is to attack Western, not just US interests".
|Michael Singh, a former White House official, talks to Al Jazeera on Interpol's warning of a global security alert
Britain, Germany, France and the Netherlands said they would close their embassies in Yemen on Sunday and Monday for similar security reasons. Yemeni authorities said they were on a state of high alert.
Canada also announced that it would close its mission in the Bangladeshi capital of Dhaka.
The US has also issued a global travel alert to warn its citizens of potential "terrorist attacks".
A heavy military presence was reported around the US and British embassies in Yemen's capital Sanaa on Saturday, with numerous checkpoints.
In London, the Foreign Office said that a number of staff at the British embassy had been withdrawn from Sanaa, particularly because of increased concerns in "the final days of Ramadan and into Eid". France and Germany cited instability for their decisions in Yemen.
In Washington DC, meanwhile, top US officials met to review the threat, with President Barack Obama briefed following the session.
Interpol, in issuing its alert, said it suspected al-Qaeda was involved in recent jailbreaks across nine countries, including Iraq, Libya and Pakistan. The global police agency said the jailbreaks had "led to the escape of hundreds of terrorists and other criminals" in the past month alone.
The alert calls on Interpol's 190 member countries to help determine whether these events are coordinated or linked, the organisation said in a statement on Saturday.
'Threat very strong'
In Yemen, at least one person died and six others were wounded in clashes on Friday between soldiers once loyal to Ali Abdullah Saleh, Yemen's toppled president, and a rival army faction in Sanaa, police and medical sources said.
The friction added to rising tension in Yemen, which is increasing because of renewed drone attacks and security concerns.
The threat of al-Qaeda is very strong right now
Hakim Almasmari, editor of the Yemen Post, told Al Jazeera that the country is at its most tense for a year.
"[This is] mostly due to the lack of security presence in the government and because of drone strikes taking place this week," he said.
At least three have struck Yemen in the past seven days, killing 13 people including civilians, he said.
"The timing of the strikes was very unfortunate" further compounding the impact on Yemeni people, Almasmari said, because they fell in the month of Ramadan and as President Abd-Rabbu Mansour Hadi was on a trip to the US.
"The threat of al-Qaeda is very strong right now," he said.