Britain is due to close its embassy in Yemen on Sunday amid heightened security fears after the US issued a global travel alert because of a threat of possible al-Qaida terrorist attacks.

The two-day closure, described by the Foreign Office as a "precautionary measure", came amid concerns over escalating violence in the country.

The US state department issued the alert because of a threat of attacks during August, particularly in the Middle East. Some 21 US embassies in the region – including Yemen – will close. France and Germany were also shuttering their diplomatic missions in Sana'a.

Interpol, meanwhile, issued a global security alert on Saturday in connection with suspected al-Qaida involvement in several recent prison escapes including those in Iraq, Libya and Pakistan. The alert calls on its 190 member countries to help determine whether these events are co-ordinated or linked.

Clashes were reported in Sana'a on Friday. Military officials said one fighter was killed and six were wounded in the unrest.

The casualties were reported to be part of a rebel group of Republican Guard troops loyal to Yemen's ousted president, Ali Abdullah Saleh.

There has been a rise in attempted abductions and carjackings of foreigners in Sana'a in recent months and US drone strikes in Yemen have been blamed for escalating tensions as President Abdo Rabbo Mansour Hadi met President Barack Obama in Washington for talks last week.

The Foreign Office has issued stark warnings urging any British citizens in Yemen to leave. Its advice reads: "If you don't leave the country now while commercial carriers are still flying it is extremely unlikely that the British government will be able to evacuate you or provide consular assistance.

"The situation in Yemen remains volatile, with continuing unrest and violent clashes. The threat of an escalation of violence and disorder remains.

"If you travel to Yemen against our advice, you should regularly reassess your security and plan any movements around the country carefully. The provision of close security protection and/or a military escort is extremely important for those working and moving around in Yemen."

The Foreign Office recommended particular vigilance during the Muslim holy month of Ramadan – which ends on 8 August – when "tensions could be heightened".

A security source in Sana'a said: "IEDs [improvised explosive devices] were discovered in and around the capital at checkpoints that lead to and from the embassies of the UK and the US. This prompted the capital's security forces to think their security protocol was being 'tested' for a larger attack."