The US was not being "unreasonable" in refusing to release the last Britons at Guantanamo Bay, Tony Blair said.
Detainees at Guantanamo
He said he was not sure that security "machinery" was in place in the UK to ensure the detainees posed no threat.
Mr Blair told the Commons liaison committee he hoped the issue would be resolved "reasonably soon".
"I do not think the US is being unreasonable in saying we need to make sure there is security in place for these people," he said.
"There is an issue about these particular people in respect of the United States that is not just about their status as detainees and we need to be very clear - I actually need to be very clear in respect of our own country - that we are not putting anyone at risk.
"I am not yet satisfied that we have the necessary machinery in place but we are working on that.
"We all know that we are faced with a significant terrorism threat. These people were picked up in circumstances where we believe at the very least there are issues that need to be resolved, let us say, in respect of those individuals.
"Certainly from what I have seen about those individual cases I would need to be very, very clear that there was in place in this country a sufficient infrastructure and machinery to be able to protect our own security."
Mr Blair said he had spoken to President Bush recently about getting the British detainees freed.
He said: "We feel somewhat hindered in our explanation to people. It would be easy to read explanations in some parts of the media and say 'what have they done?'.
"I just have to be careful in terms of the security of this country.
"These things did not arise out of some sort of random event."