The US is increasing the number of air marshals travelling on flights between the US and UK following three failed car bomb attacks in London and Glasgow.
The attack in Glasgow has forced a reassessment of targets
Homeland Security head Michael Chertoff said security would also be beefed up on flights to and from mainland Europe.
He said the US threat level would stay at orange - its second highest level - but that security would be tightened on all US travel networks ahead of 4 July.
France is also bolstering security in the wake of the attempted UK bombings.
Interior Minister Michele Alliot-Marie said that although there was no specific intelligence to suggest France could be next "it is obvious that France, like a number of other countries, is a potential target of terrorism".
She was speaking after a top-level security meeting in Paris which brought together senior members of France's intelligence services, national police force and border police.
On Saturday, President Nicolas Sarkozy sent a letter to new UK Prime Minister Gordon Brown saying that "in this implacable fight against terrorism, our countries are not only unfailingly united but also in close and constant co-operation".
On Sunday, US President George W Bush said he welcomed the UK government's "strong response" to the attacks.
"It just goes to show the war against these extremists goes on," Mr Bush said. "You never know where they may try to strike, and I appreciate the very strong response that the Gordon Brown government's given to the attempts by these people."
Speaking on a series of US TV chat shows over the weekend, Mr Chertoff said the US was increasingly worried about threats originating in Europe.
He particularly spoke about Europeans going to terror training camps in South Asia then returning to Europe to use it as a staging post for attacks in Europe or the US.
Security is being raised at all travel hubs ahead of the 4 July holiday
Mr Chertoff said that UK attacks had forced a reassessment of security precautions:
"We haven't singled out Glasgow until a couple of days ago as a particular location for focus, but there has been a strategy of mixing up the deployment of these air marshals, sometimes more in one destination, sometimes more in another destination," he said.
"Going forward, we will be doing some enhanced air marshal work and similar types of activities with respect to UK travel."
Mr Chertoff said that although there were concerns that there could be copy-cat incidents in the US that the country's security level would remain as it is, at orange - the second highest threat level.
However, he said that as a matter of course there would be a tightening of security at airports, railway stations and other travel hubs as the 4 July holiday weekend approached.