Britain and France will work together more closely on nuclear defence, Prime Minister Gordon Brown said Friday, after a report that the two countries could share submarine patrols.

Brown said he had reached an agreement with French President Nicolas Sarkozy on nuclear cooperation during Sarkozy's visit to London last week.

"UK and French cooperation is at its highest level," he told reporters in London.

"We have agreed a degree of co-operation that is, I think, greater than we have had previously but we will retain, as will France, our independent nuclear deterrent".

Brown gave no further details, but he stressed that he and his government "do not see the case for us withdrawing the independent nuclear deterrent that we have".

His comments came as the Guardian newspaper reported that France has offered to create a joint nuclear deterrent with Britain by sharing submarine patrols, but London has so far opposed the idea as politically unacceptable.

Both Britain and France now follow a system of continuous at-sea deterrence, running at least one nuclear-armed submarine which is submerged and undetected at any given time.

But the system has faced criticism from disarmament campaigners who question its use in a post-Cold War world.

Brown -- who faces a general election in Britain likely on May 6 -- has previously said Britain is prepared to reduce its number of submarines which can launch nuclear missiles as part of global disarmament efforts.

The United States is hosting an international summit on nuclear security in Washington on April 12-13.