US authorities could soon demand more information about passengers leaving Europe for airports in the United States and seek to keep the details for longer, a senior US official said Tuesday.

Speaking a day after the European Union endorsed an interim deal to give more US law enforcement agencies access to passenger name record (PNR) data, the official refused to rule out a demand within months for more information.

"We are prepared to review that. That's an issue that deserves a look but I don't come with a list of additional items," said Stewart Baker, Assistant Secretary for Policy at the US Department of Homeland Security.

The interim deal, reached early this month after lengthy talks and days after a legal deadline had passed, will allow US agencies involved in fighting terrorism -- such as the FBI -- conditional access to passenger data.

Critics say the deal, to run until July, with US and EU negotiators starting work as soon as January on a more permanent agreement, saw Brussels cave in to Washington's demands.

The 34 pieces of data include credit card and passport details, e-mail addresses and travel itinerary, but Baker played down concerns that the information being sought was too personal.

"I question how interesting this is," he told journalists in Brussels. "It is not ordinarily our deepest secret."

When asked how long the US customs authorities, which handle the information provided by European airlines, would want to keep the data, he said: "As long as it would be likely to be relevant."

US law enforcement data is usually kept for about 40 years, he noted.

Another potential can of worms would be a demand to provide travellers with a warning about what kind of information they were providing so they could decide whether they really wanted to travel to the United States.

"If you don't want to give up the information then you don't need to take the trip to the United states, and that might be more controversial" for the Europeans, Baker said, without elaborating.

The previous accord, from 2004, was outlawed by Europe's top court and the deadline for renewing it expired on October 1, leaving airlines in an uncomfortable legal limbo.

After the interim deal was reached, EU lawmakers said it was the "least worst option" and one that was made to stop chaos on airlines.

US authorities are "determined to extract ever more personal data and share it with the wider intelligence community. It is important that we agree where we stand here," said Graham Watson, leader of the EU assembly's liberals group.

Baker too was critical, saying it was too elaborate and that it almost amounted to "a code of conduct for the United States."

"We need to establish something that's a little closer to the more normal relationship between democracies", he said, like acknowledging that US and EU societies are based on foundations including respect for rights and liberties.

The problem surrounding the data transfers has its roots in intelligence failures that contributed to the success of the September 11, 2001 suicide plane hijackings in the United States.

The US Congress endorsed closer cooperation between law enforcement agencies but that conflicted with European reluctance to give open access to information about its citizens, particularly when their rights are not so well protected.