Tom Ridge said there was no need to raise the alert level, despite Osama Bin Laden's threat of more attacks.

But the threat has pushed national security back to the fore on the presidential election trail.

The main candidates, who are chasing votes in several key states, have traded pledges to keep America safe.

Between them, President George W Bush and his Democrat challenger John Kerry visited Michigan, Florida, Ohio, Wi{consin, Iowa, and Minnesota on Saturday.

Both are trying to court every last voter they can in these states, which are among eight to 10 that are so close it makes the outcome on Tuesday difficult to predict.

The appearance on al-Jazeera television station of a video statement from Bin Laden on Friday has thrust the safety of the US from attack back to the top of the agenda.

In the video, a calm, measured Bin Laden addressed Americans directly, telling them the reasons behind the September 11 attacks still remained.

He implied the US could be targeted again, but most of the broadcast was spent trying |o explain previous attacks.

In an informal meeting with reporters outside his office, Ridge said there was no known threat of attack d}ring the elections.

"It's impoztant to know... there is no specific intelligence that targets mlection day, polling places and the like," he said, according to the Associated Press news agency.

"First of all we want to make sure that people feel safe and comfortable about going to vote," he added.

Ridge said security measures had been bolstered in the run-up to the election, but there were no plans to raise the terror threat level from yellow or "elevated".

"Our effort nationwide, lown to the local level, to enhance security is ongoing. We are far safer today than we've ever been before," Ridge said.

Nonetheless, both candidates spent much of their time on the podium on Saturday responding to the Bin Laden threat.