The United States is satisfied with its current terrorism alert level and acknowledges potential al-Qaida links to the plots in Britain, Homeland Security Secretary Michael Chertoff said yesterday.

"I think given what we know now, we're comfortable that we're at the right posture," he said during a round of talk show appearances.

In response to an attack at a Scottish airport and two foiled car bombs in London, US airports and mass transit systems are tightening security ahead of the Fourth of July holiday.

Airports are at the second of five security threat levels - orange - indicating a high risk of terrorist attacks. The current national threat level is yellow, or the third highest, indicating an elevated threat.

Chertoff said he does not plan to change those levels. "At this moment we don't have a specific credible threat against the United States," he said.

The Transportation Security Administration is posting more agents outside terminals at some airports, White House spokesman Tony Snow said.

"There will be some inconvenience of passengers in terms of longer wait times," Snow said. Local police also may take separate measures, he added.

Source: China Daily/agencies