The British embassy in Yemen is to shut temporarily and several other embassies have been told to be vigilant after the US issued a terrorism warning.
The embassy in Sanaa will be closed on Sunday and Monday, as will the embassies of France and Germany.
The US reportedly intercepted al-Qaeda messages and will shut at least 21 embassies and consulates on Sunday.
Interpol issued a separate global security alert, citing jail breaks linked to al-Qaeda in nine countries.
The international policing organisation said "hundreds of terrorists" had been freed during breakouts in countries including Iraq, Libya and Pakistan in the past month.
Interpol said al-Qaeda was suspected of "involvement in several of the breakouts" and asked its 190 member states to help "determine whether any of these recent events are co-ordinated or linked".
The British embassy in Yemen had already been operating with a reduced staff "due to increased security concerns".
A Foreign Office spokesman said the closure was a "precautionary measure" and would not say if it was due to a specific threat, but a number of British embassies in the Middle East have been warned about increased risks.
Security analyst Peter Bergen said militant group al-Qaeda had previously showed "strong interest in launching attacks" on the 27th day of Ramadan, which is on Sunday.
Robin Simcox, a research fellow at the Henry Jackson Society, which monitors threats from al-Qaeda, told the BBC he believed US authorities had intercepted communications "between senior al-Qaeda leaders talking about an operational and clearly viable plot against an embassy".
The claim was reported by the New York Times.
Mr Simcox said it was unclear which embassy was to be targeted, but Yemen is a high-risk country because al-Qaeda's "most active franchise" is based in the Arabian Peninsula and the US has stepped up drone attacks in Yemen in recent days.
He said there had been a "lull" in the drone attacks in Yemen in the past two months, and said the sudden increase suggested the latest threat was "emanating from Yemen itself".
Hundreds of Britons are thought to be living in the country.
A Foreign Office spokesman said: "We keep travel advice and the security of our staff and missions under constant review.
"Our travel advice advises particular vigilance during Ramadan, when tensions could be heightened. We are particularly concerned about the security situation in the final days of Ramadan and into Eid."
The Islamic holy month ends next week.
Shadow foreign secretary Douglas Alexander said: "The government must also now urgently review security at Britain's other postings in the region given moves by other countries to withdraw staff for their security."
Iona Craig, the Times' correspondent in Yemen, said very few British people now remain in the country, mostly working for the embassy, charities, UN organisations and oil companies.
She said "the threat to foreigners here has definitely increased" in recent months.
She told BBC Radio 4's Today programme British embassy staff in Yemen now live on-site, following two attacks in 2010.
- In April 2010, a suspected al-Qaeda suicide bomber tried to kill the British ambassador to Yemen in Sanaa. No-one except the attacker was killed.
- In October 2010, militants fired a rocket-propelled grenade at a car carrying Britain's deputy ambassador in the Yemeni capital. One embassy worker and two bystanders were injured.
On its website, the Foreign Office was already advising against all travel to Yemen and urging British nationals to "leave now".
It says there is "a high threat from terrorism throughout Yemen" and "a very high threat of kidnap from armed tribes, criminals and terrorists".
Unlike the US, the UK is keeping its embassies in Saudi Arabia, Oman, Qatar, Bahrain, Kuwait, United Arab Emirates and Iraq open, but it has advised staff to "exercise extra vigilance".
In a statement, the US state department said: "Current information suggests that al-Qaeda and affiliated organizations continue to plan terrorist attacks both in the region and beyond, and that they may focus efforts to conduct attacks in the period between now and the end of August."
The US issued a global travel alert on Friday, saying al-Qaeda was planning attacks.
BBC state department correspondent Kim Ghattas said it was "not unusual" for the US to issue travel warnings, but said "this one is both wide-ranging and somewhat specific".