It is too early to tell whether British-born Pakistanis were among the Mumbai terrorists, Gordon Brown said today in response to claims that at least two Britons were involved.

The Foreign Office is investigating reports on the Indian channel NDTV quoting Vilasrao Deshmukh, the chief minister of Maharashtra state, as saying there were British nationals among the militants arrested.

In a televised address yesterday, the Indian prime minister, Manmohan Singh, said the attacks had "external links", which was interpreted as a reference to Pakistan.

Brown said today that he would talk to Singh about the claims of British involvement. "I would not want to be drawn into early conclusions about this. 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 this morning," he told Sky News.

"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 cooperation between India and Britain in dealing with these instances of terrorist attacks."

It is understood that in recent years dozens of British-born Pakistanis have travelled to Pakistan to train in terror camps.

The foreign secretary, David Miliband, said that British authorities were working "intensively" on establishing the origins and identities of the terrorists. "We obviously will want to work very, very closely with the Indians on that, but it is too early to say whether or not any of them are British," he told Sky News.

The home secretary, Jacqui Smith, said UK authorities had "no knowledge" of any British links with the attacks.

"We will do anything we can to help Indian authorities through what is obviously a very difficult time," she said. "We will do what is necessary. At the moment the priority is to support the immediate needs. We will work with the Indians to see what we can learn from the events."

Indian commandos have recovered credit and identity cards belonging to the militants, which may shed more light on their nationalities.

Security services in Britain are studying images of the attackers in an effort to identify them. But a Foreign Office spokeswoman said the department was "not aware of anything giving any credence to those reports at the moment".

A team of Scotland Yard anti-terrorist detectives and negotiators are now on their way to Mumbai to assist the Indian authorities.

Deshmukh, said up to 25 gunmen were responsible for the series of bomb blasts and shootings that targeted tourists and foreign interests.