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Iran on Monday dismissed "unfounded" accusations by newly appointed US Secretary of State Mike Pompeo over its "ambition to dominate the Middle East".

Pompeo lashed out at Tehran on Sunday during his whistle-stop tour of America's Middle East allies ahead of a crucial White House decision on whether to quit a landmark 2015 nuclear deal with Iran.

Speaking during a visit to Iran's arch-rival and key US ally Saudi Arabia just days after he took office, Pompeo accused Tehran of destabilising the Middle East through its support for Syria's President Bashar al-Assad and for rebels in Yemen.

"The US secretary of state's remarks on the presence and role of the Islamic Republic of Iran in certain countries in the region are a repetition of absurd and unfounded accusations," Iran's foreign ministry spokesman Bahram Ghassemi said in a statement on Monday.

Iran's presence in Syria and Iraq is in response to requests from the two countries' Shia-allied governments and is part of "the fight against terrorism in the region", he said.

"This assistance will continue as long as [these] governments need help in this fight," he said.

Ghassemi also reiterated previous government statements denying Saudi and US accusations that Iran is supplying weapons to Yemen's Houthi rebels, who are backed politically by Tehran. 

Read more: Trump's hawks will try to destabilise Iran

Such charges are "a false problem, created solely for the purpose of diverting the attention of international public opinion from the atrocities committed by Saudi Arabia in its daily attacks" in Yemen, he said.

Shia theocracy Iran and Sunni heavyweight Saudi Arabia, which cut diplomatic ties in January 2016, are engaged in a region-wide struggle for influence and back rival sides in Lebanon, Syria and Yemen.

Tehran has deployed "military advisors" and thousands of Iranian and Afghan "volunteer" fighters to Syria and Iraq.

Saudi Arabia launched a military coalition in 2015 to battle the Shia Houthi rebel group in Yemen who had seized the capital Sanaa the previous year.

The United Nations and rights groups have slammed the Saudi-led campaign for causing civilian casualties and sparking a humanitarian crisis through its blockade of Yemen's ports.

In a related development, Russian President Vladimir Putin and French leader Emmanuel Macron on Monday voiced their staunch support for the Iran nuclear accord, calling for "strict observance" of the 2015 deal, as US President Donald Trump still deciding on whether to scrap the agreement.

"The Presidents of Russia and France spoke in favour of keeping the Plan and its strict observance," the Kremlin said, referring to the Joint Comprehensive Plan of Action. The statement was released after Macron called Putin to inform him of his talks with Trump in the United States.

Pompeo, a close aide of Trump, has been a vociferous opponent to the Iran nuclear deal, with many expecting him to encourage the president to scrap the historic agreement.