TEHRAN (Reuters) -- Iran's Supreme Leader Ayatollah Ali Khamenei accused the United States on Tuesday of promoting terrorism in border areas and using arms and money against the Islamic state.

Khamenei's verbal attack is likely to disappoint U.S. President Barack Obama's administration, which is seeking rapprochement with Iran after three decades of mistrust. The Pentagon said his comments were "terribly ironic" because Tehran was undermining stability in neighboring Iraq and Afghanistan.

Khamenei was speaking in a western region close to Iraq where security forces often clash with Kurdish separatist rebels. Iran has also in the past accused its Western foes of seeking to destabilize it by backing insurgents on its borders.

"I say this firmly that unfortunately across our borders, our western borders, the Americans are busy making a conspiracy, they are busy fostering terrorism," he said, referring to the U.S. presence in Iraq, Iran's western neighbor.

"Money, arms and organization ... are being used by the Americans directly across our western borders in order to fight the Islamic Republic's system. We should be awake," he said during a visit to Iran's Kurdistan province.

Like Iraq and Turkey, Iran has a large Kurdish minority, mainly living in its northwest and west. Kurdish guerrillas based in remote mountainous areas in Iraq close to Turkey and Iran have long been a source of regional instability.

Khamenei spoke a day after Obama said he wanted to see serious progress on his diplomatic initiative toward Iran by the end of the year. Obama also held out the prospect of tougher sanctions against Tehran "to ensure that Iran understands we are serious."

"TERRIBLY IRONIC"

The Pentagon said Khamenei's comments were "terribly ironic given the fact that the Iranians continue to provide financing and weaponry to undermine our efforts to stabilize the governments in Iraq and Afghanistan."

Asked specifically whether he denied the Iranian accusation that the U.S. military was financing efforts to destabilize Iran, Pentagon press secretary Geoff Morrell replied: "It's not to my knowledge that we are undertaking anything of that sort."

Washington and its Western allies suspect Iran's nuclear program is aimed at making bombs, a charge Tehran denies. But in a break with his predecessor George W. Bush's approach, Obama has offered direct talks with Tehran to resolve the dispute.

Iran says Washington must show a real policy shift toward it. The mainly Shi'ite Muslim country has seen its regional influence grow since the 2003 ouster of Sunni strongman Saddam Hussein in Iraq, sparking unease among Sunni Arab powers.

In other comments underscoring deep suspicion of the United States, Khamenei last month blamed U.S. forces for two bombings that killed dozens of Iranian pilgrims in Iraq.

Ali Ansari of the University of St Andrews in Scotland said he believed Khamenei was trying to "rein in" moderate candidates in Iran's June 12 presidential election who are advocating constructive talks and better ties with the West.

He said Khamenei was "ideologically disinclined" to relations with Washington but was not closing the door to a possible opening. The United States cut bilateral ties shortly after Iran's 1979 Islamic revolution.

Khamenei on Monday urged Iranians to support anti-Western candidates, without openly supporting Ahmadinejad who is a vocal opponent of western policies.

"Do not let those who would ... surrender to enemies (the West) and harm our nation's prestige to get into office," Khamenei said in a televised speech in the western city of Bijar.

In Tuesday's speech in Kurdistan, Khamenei said the United States had "dangerous plans" for Kurdish-populated areas.

"Anywhere they (the Americans) can, they stretch their hands in order to put their contemptible and bloody claws into the body of the Kurdish people," Khamenei said.

By Zahra Hosseinian

Writing by Fredrik Dahl; Additional reporting by Fredrik Dahl in Tehran and Andrew Gray in Washington; Editing by Dominic Evans.