File photo. Photograph:( Reuters )
The Foreign and Commonwealth Office said that terrorists 'are very likely' to try to carry out further attacks, which 'could be indiscriminate, including in places visited by foreigners.'
Britain on Thursday warned against "all but essential travel" to Sri Lanka following the terror attacks on Sunday that claimed 253 lives according to the latest toll.
"The Foreign and Commonwealth Office (FCO) advise against all but essential travel to Sri Lanka, due to the current evolving security situation following attacks on 21 April 2019," the ministry said on its website.
It added that terrorists "are very likely" to try to carry out further attacks, which "could be indiscriminate, including in places visited by foreigners."
"The extent of any continued threat following the 21 April attacks remains unclear," it said.
The Netherlands later also updated its travel advice for Sri Lanka, telling Dutch citizens they should only go there "if necessary".
Eight British nationals and three with Dutch citizenship were among those killed in the deadly Easter bombings that targeted tourists and Christian worshippers.
Over 250,000 Britons visited Sri Lanka in 2018, making it the third-highest source of tourism behind India and China, with the two countries retaining strong links since Sri Lanka became independent of colonial rule in 1948.
The British government told its citizens already in the country to "remain vigilant, keep up to date with developments, follow the advice of local security authorities... keep a low profile and avoid crowded public places."
"All of the attacks on 21 April were carried out either in places of worship or in places where foreign visitors were affected.
"Any further attacks may be targeted against similar locations," it warned.
A small team of specialist officers from Britain's Metropolitan Police have been deployed to Sri Lanka to support families of victims and repatriate their bodies, the force said on Tuesday.
The police said they were not helping with the investigation "at this stage", but added that "should any request come... then this will be considered accordingly."
Prime Minister May offered help in the investigation to Sri Lankan counterpart Ranil Wickremesinghe during a telephone call on Tuesday.