Washington, Aug 21 - There is more embarrassment for former US president George W. Bush as his first homeland security secretary Tom Ridge says he was pressured to raise security threat levels before the 2004 election to influence voting.

When Bush sought re-election in 2004, he and his Democratic rival John Kerry were neck and neck in the race to the White House.

But just four days before the polls, Osama bin Laden had issued a tape warning Americans against voting for Bush.

It has been speculated that the tape helped Bush win the second term in the White House.

Now in his memoir, 'The Test of Our Times: America Under Siege...and How We Can Be Safe Again', Ridge says he was pressured by then defence secretary Donald Rumsfeld and attorney general John Ashcroft to raise security levels after the bin Laden tape.

But he refused to budge, says Ridge in the book, thinking it was 'politically motivated'.

America's first-ever home security chief has been quoted as calling this event 'dramatic and inconceivable'.