Islamic State militants are operating Brussels-style terror cells in England, according to the director of US National Intelligence James Clapper.

Speaking at a briefing with journalists in the US, Mr Clapper also said IS has taken advantage of Europe's migration crisis.

He said there was a "fundamental conflict" between national security and free moment throughout the European Union.

Asked if IS cells like those in Brussels exist in England, Germany and Italy, he replied: "Yes, they do. That is a concern of obviously ours and our European allies.

"We continue to see evidence of plotting on the part of ISIL in the countries you name.

"They (IS) have taken advantage to some extent of the migrant crisis in Europe, something which the nations have a growing awareness of."

Clapper was speaking at a briefing hosted by the Christian Science Monitor, and said the US is "doing all we can" to share information with foreign counterparts.

"The obstacles in Europe have somewhat to do with some of the fundamental conflicts between, on the one hand, European Union incentives and drives to promote openness and free movement of people and goods."

He added that free movement was "in conflict" with the responsibility of nations to protect its borders and citizens' security.

(Sky News)