NEW YORK, July 1: Following Saturday’s attack on Glasgow airport, the United States is increasing its security at airports and other ports of entry which will include more air marshals on flights to UK, Homeland Security Secretary Michael Chertoff said on Sunday.

Counter-terrorism officials also said it was too early to dismiss an Internet message posted to an Islamic forum on Thursday that threatened attacks on London in retaliation for the award of a British knighthood to Salman Rushdie.

On Sunday, a day after US officials responded to the Glasgow attack by raising security at airports, Mr Chertoff told ABC news channel that there remained “no specific credible evidence” of a threat against the US.

He said US authorities would tighten security “at various rail locations and other mass transit locations” this week as many Americans prepare to travel for the Independence Day holiday on July 4.

In a sign of security fears, the New York Port Authority briefly evacuated the American Airlines terminal at John F. Kennedy International Airport on Sunday as it investigated a suspicious package. Officials later gave the “all clear”.

“Since the events of the last couple of days we will be doing so for some time,” he said.

A US counter-terrorism official told reporters that the incidents in Britain could encourage so-called copy cat actors by demonstrating how attacks might be carried out with common materials.