Republican White House hopeful John McCain has promised to apply massive diplomatic and financial pressure on Iran if elected president.

Normally a proponent of hawkish policies, McCain told MSNBC's "Hardball" on Tuesday that it would be difficult to convince the American people to go to war against Iran.

"I believe we can act with nations with values and principles that we hold dear and exercise enormous pressure -- diplomatic, trade, financial," Reuters quoted him as saying.

If he decided he had to attack, McCain said he would have to make an "even more convincing argument that it was necessary to do so because of our failure to find weapons of mass destruction," in Iraq.

"There's a little credibility gap," he said, referring to President George W. Bush, who justified the 2003 invasion of Iraq by saying it possessed weapons of mass destruction.

MGH/DT