The European Commission has rejected a call by the European Parliament to review restrictions on taking liquids on board aeroplanes.
MEPs said banning liquids from flights might not be cost-effective
It said the restrictions could not be relaxed if there was still a threat that liquid explosives would be used for terror attacks on planes.
Earlier the European Parliament adopted a resolution calling on the EC to review the regulation.
It said the security benefits may not justify the cost of the ban.
"The understanding and the readiness with which the vast majority of our citizens have accepted this measure and the inconvenience it brings are the best proof that they consider it to be adequate and necessary," EU Transport Commissioner Jacques Barrot said.
He added "Europe must not show any sign of weakness" in the face of terrorist threats.
"It must not lower its guard but on the contrary reinforce its vigilance and maintain the full range of prevention instruments it has adopted," Mr Barrot said in a statement.
His comments come on the day Germany announced it had foiled a major terrorist plot against US targets in the country.
The parliamentary resolution calls for the ban on passengers taking liquids on planes in containers of less than 100ml to be lifted.
It is purely advisory as members of the European Parliament (MEPs) have no power to impose any measures.
"The European Parliament is concerned that the cost [of] the regulation may not be proportionate to the added value in terms of additional security," the resolution said.
The regulation was brought in after police in London said they had broken up a plot to bring down as many as 10 planes using liquid explosives.