Tehran: Iran warned the United States yesterday it would find itself in a "quagmire deeper than Iraq" if it attacked the Islamic state, and Russia stepped up efforts for a diplomatic solution to Tehran's nuclear row with the West.

The warning by the head of Iran's elite Revolutionary Guards, a target of new US sanctions announced last week, added to angry rhetoric between the two old foes that has prompted speculation of possible US military action.

US President George W. Bush this month suggested a nuclear-armed Iran could lead to World War Three but the White House said on Tuesday it remained determined to resolve the stand-off peacefully.

"If the enemies show inexperience and want to invade Islamic Iran, they will receive a strong slap from Iran," Jafari said in comments carried by the semi-official Fars News Agency.

"The enemy knows that if it attacks Iran it will be trapped in a quagmire deeper than Iraq and Afghanistan, and they will have to withdraw with defeat," he told a parade in north-central Iran, without mentioning the United States by name.

Major powers are expected to meet in London this week to discuss a possible third round of UN sanctions against Iran over its refusal to halt work which it says is aimed at generating electricity but could also be used for making bombs.

Iran agreed with the UN International Atomic Energy Agency (IAEA) in August to clear up suspicions about its past secret nuclear activities.

The United States, saying the deal failed to address the core UN demand that Tehran suspend work Washington suspects is aimed at making bombs, is pushing for tougher UN sanctions. Tensions over Iran's nuclear programme are one of the factors that have pushed oil prices to record highs of over $90 a barrel in recent days.

Russia, a veto-wielding member of the UN Security Council, says dialogue rather than punishment or talk of military action offers the best way to ease tension. It says the IAEA process should be given time to run its course.

Speaking after talks with Iranian President Mahmoud Ahmadinejad on Tuesday evening, Russian Foreign Minister Sergei Lavrov said, according to a transcript from his ministry: "We encouraged the Iranian leadership to undertake further -- and preferably more active - work with the IAEA to clear up those questions which have been raised by the agency with regard to the Iranian nuclear programme's past."

Lavrov, visiting two weeks after a trip to Tehran by President Vladimir Putin, said he "underlined the importance of closing these questions as soon as possible, in order to restore trust in the exclusively peaceful nature of Iran's activities."

Security Council members to meet

US officials said they expected the five permanent UN Security Council members - the United States, Britain, France, China and Russia - as well as Germany to meet later this week in London to discuss new sanctions. Britain and France back a tough line on Iran. China, like Russia, has opposed an early move to tighten economic sanctions, saying Iran should be given longer to cooperate with the International Atomic Energy Agency.