Claims that Britons were among the attackers in Mumbai were being investigated by the Foreign Office.
As Indian troops cleared the last terrorists from buildings across Mumbai, UK authorities were following up reports on local news channel NDTV that the terrorists included "British citizens of Pakistani origin".
The claim was made as Gordon Brown called for improved international action against terrorism following the Mumbai attacks.
He said that as far as the Government was aware, there were no British hostages still being held in the Indian financial capital.
And he said ministers were determined to do what they could to help the Indian authorities dealing with the attacks.
"It is clear that we have got to help the Indian government deal with this terrorist incident and we have sent people from the Metropolitan Police to help," he told Sky News.
"This is an atrocious outbreak of violence planned in advance and I think we have got to look at how international action against terrorism can be improved over the next period of time."
Mr Brown said he would be discussing the attacks with Indian prime minister Manmohan Singh following claims by the Indian government that the attackers came from outside the country.
"There is so much information still to be discovered and made available. I have heard what Prime Minister Singh has said and I'll talk to him about it," Mr Brown said.
"But obviously when you have terrorists operating in one country, they may be getting support from another country or coming from another country, and it is very important that we strengthen the co-operation between India and Britain in dealing with these instances of terrorist attacks."
Mumbai gunmen 'included Britons'
The Press Association