The United States wants the European Union to pool data on airline passengers to bolster security and prevent Islamist extremists from staging attacks on the West, US officials told lawmakers Wednesday.

The mounting numbers of foreign fighters flocking to Syria to join forces with militants has raised concerns on both sides of the Atlantic that jihadists with Western passports could slip through borders without being detected.

US counter-terrorism officials said a key tool to track militants and disrupt plots was sharing information on airline passengers, known as passenger name records (PNR).

Francis Taylor, undersecretary for intelligence and analysis at the Department of Homeland Security, said Washington was "encouraged" by discussions in the European Parliament to permit the pooling of passenger data throughout the European Union.

There was a "hope that the European Parliament will move forward to pass a European-wide PNR requirement that allows for that data to be collected across Europe and shared across the EU," Taylor told the House Committee on Homeland Security.

"We think that will be a big step."

He added that "if that doesn't work, then we can work bilaterally with individual countries to share data."

In the wake of extremist attacks in Paris that left 17 dead, European, US and Canadian interior ministers said there was a "crucial and urgent need" to establish an EU-wide database of passenger information for travel inside Europe -- and for flights leaving or entering the 28-nation bloc.

At the House hearing, the head of the National Counter-terrorism Center, Nicholas Rasmussen, said there has been "a fairly dramatic improvement" in sharing intelligence on potential suspects among US and European spy services.

"I would argue that a couple of years ago we were in the position of explaining, 'Gee, this is a terrible threat, we need to work together on it.'

"We're well past that now."

While European intelligence services were often eager to pass along information on known jihadists, the question of sharing large amounts of more general data remained problematic, according to Rasmussen.

He said "there's a kind of bulk data-sharing discussion that is sometimes more difficult for our European partners."

The European Parliament is due to take up a bill this week that would require airlines to provide EU governments air travel data on passengers. The proposal was blocked in 2011 amid concerns over privacy rights.

After the deadly attack on the satirical magazine Charlie Hebdo in January in Paris, French Prime Minister Manuel Valls said the country would begin collecting airline passenger data by September.