Attacks on the graves of British servicemen in Benghazi, Libya, have been described as “horrific” by Foreign Office Minister Alistair Burt.
The Foreign Office said 200 graves and a Cross of Remembrance were damaged at the Benghazi British Military Cemetery.
The Benghazi War Cemetery was also targeted. Both cemeteries commemorate British and Commonwealth nationals who died during or after World War II.
The Libyan authorities apologised and pledged to catch those responsible.
The damage was “unethical, irresponsible and criminal”, the ruling National Transitional Council said.
The Foreign Office said it now believed the attack was carried out by militant islamists, known as Salafists, after Muslim shrines were also targeted.
“It’s horrific and wrong and we have expressed to the Libyan authorities our profound distress at what has happened on behalf of those who have loved ones there,” Mr Burt told the BBC.
“The Libyan authorities have responded in kind. They are horrified by what has happened.
“These are not actions carried out by the government of Libya, this is an extremist mob that has done this and we all share the same revulsion for it.”
Video footage made by the attackers showed about a dozen armed men kicking down headstones and trying to damage the cross.
The BBC’s Gabriel Gatehouse, in Tripoli, said the attackers referred to “Christian dogs” and a Jewish memorial was also targeted.
Our correspondent said the attack was “calm, almost casual”.
An earlier theory was that it could have been retaliation for the burning of the Koran by US soldiers at a military base in Afghanistan last month.
‘Broken and disfigured’
The Benghazi War Cemetery, which was vandalised first and where the footage was taken, contains the remains of servicemen killed during World War II.
There are 1,214 Commonwealth servicemen buried or commemorated there, with 851 British deceased among the 1,051 identified graves.
The Benghazi British Military Cemetery has 284 burials, 11 of them unidentified.
The Commonwealth War Graves Commission (CWGC) said on its website that headstones were “broken and disfigured” at both cemeteries, which are roughly a mile apart.
A spokesman said the organisation was “deeply saddened” by the incident.
The BBC understands that at some point during the attack on the British Military Cemetery a group of older people intervened, preventing further damage.
The CWGC said it would conduct a full survey of the damage at both cemeteries once it was safe to do so.
“Both cemeteries will be restored to a standard befitting the sacrifice of those commemorated at Benghazi, but this could take some time because we will need to source replacement stones,” the CWGC said.
It is understood a separate attack was carried out on the Italian War Graves Cemetery, also in Benghazi.
The Foreign Office said officials from its embassy in Tripoli had visited the cemeteries and raised the issue with the Libyan Ministry of Foreign Affairs and the Benghazi chief of police.
Concerns were also raised with NTC chairman Abdul Jalil and interim Prime Minister Abdurrahim al-Keib, it said.
In response, the NTC said in a statement on its website: “Some people attacked the graves of non-Muslims in Benghazi, including the graves of some of the nationals of friendly countries, including the states of Britain and Italy.”
It adds that it “severely denounces such shameful acts and vows to find and prosecute the perpetrators according to Libyan law”.
BBC Africa correspondent Karen Allen said that up until now Commonwealth war graves had been respected in Libya, and it was sad to see attacks in Benghazi.
In November last year our correspondent reported that Tripoli War Cemetery, one of five Commonwealth war cemeteries dotted across Libya, was left untouched during the uprising.