DENVER, Colorado (AFP) — Republican John McCain scorched his rival Barack Obama in a new ad Wednesday, accusing him of seeing Iran as only a "tiny" threat and arguing he is dangerously unprepared to be president.

The Obama campaign fired back immediately, angrily charging McCain with distorting the Democrats' positions and using "tired" Republican strategies of playing politics with grave national security questions.

The McCain ad injected new bitterness into the campaign on the day that Obama is set to be formally anointed at the Democratic National Convention here as the first black White House nominee in history.

"Obama says Iran is a 'tiny' country, "doesn't pose a serious threat," said the narrator as evocative pictures of Iranian President Mahmoud Ahmadinejad and the Israeli flag flash across the screen.

"Terrorism, destroying Israel, those aren't "serious threats"?

"Obama -- dangerously unprepared to be president."

The McCain campaign has castigated Obama for his offer to sit down for talks with the leaders of US foes like Iran and Syria if he is elected president, and has adopted a hawkish foreign policy.

The advertisement is based on out-of-context quotes from remarks on foreign policy by Obama in May, in which he said Iran, Cuba and Venezuela were "tiny" countries compared to the Soviet Union.

"They don't pose a serious threat to us the way the Soviet Union posed a threat to us. And yet we were willing to talk to the Soviet Union at the time when they were saying, 'We're going to wipe you off the planet.'"

Obama spokesman Hari Sevugan responded to the McCain advertisement by linking McCain to unpopular President George W. Bush's foreign policy.

"John McCain is distorting Barack Obama's words to cover up for the fact that it's the failed Bush-McCain approach to foreign policy and the Bush-McCain war in Iraq that have strengthened Iran and endangered Israel," Sevugan said.

"While Barack Obama recognizes that Iran has been the biggest beneficiary of the war in Iraq and that the Bush-McCain fear of tough diplomacy has allowed Iran to spin 3800 centrifuges, threaten Israel, and fund terrorism, John McCain promises more of the same.

"If John McCain was serious about dealing with the threat from Iran, he would join Barack Obama's bipartisan effort in the Senate to step up sanctions on Iran instead of adopting the same tired, old Bush-Rove playbook."

---