TEHRAN: Iran on Monday played down the threat of new US sanctions as Washington was expected to tighten punitive measures on Tehran in a standoff sparked by the US withdrawal from a nuclear deal.

Tensions have flared after Iranian forces shot down a US drone Thursday, the latest in a series of incidents including attacks on tankers in sensitive Gulf waters that have raised fears of an unintended slide towards conflict.

Both the US and Iran have repeatedly said they want to avoid going to war, but the spiralling tensions saw US Secretary of State Mike Pompeo travel Monday to meet with Saudi leaders to build a "global coalition" against the Islamic republic.

Tehran says the drone violated Iranian airspace and Foreign Minister Mohammad Javad Zarif has backed the claim with maps and coordinates -- allegations dismissed by Washington.

US President Donald Trump claimed he called off a planned retaliatory military strike on Iran at the last minute, tweeting that Washington would instead place "major additional sanctions on Iran on Monday".

"Are there really any sanctions left that the United States has not imposed on our country recently or in the past 40 years?" Iran's foreign ministry spokesman Abbas Mousavi said at a Monday press conference in Tehran.

"We really do not know what (the new sanctions) are and what they want to target anymore, and also do not consider them to have any impact," he added.

Last year, Trump unilaterally pulled the US out of a landmark 2015 deal meant to curb Iran's nuclear programme in exchange for sanctions relief.

The US has since imposed a robust slate of punitive sanctions on Tehran designed to choke off Iranian oil sales and cripple its economy -- which he now plans to expand.

Trump, who has waged a "maximum pressure" campaign against Iran, has also said the US is prepared to negotiate with the Islamic republic with "no preconditions".

"America's claim of readiness for unconditional negotiation is not acceptable with the continuation of threats and sanctions," Hesamodin Ashna, an advisor to Iran's President Hassan Rouhani, said Monday on Twitter.

"We consider war and sanctions to be two sides of the same coin," he added.

- 'Global coalition' -

Pompeo met Saudi King Salman and Crown Prince Mohammed bin Salman in the Red Sea city of Jeddah and was later due to hold talks in the United Arab Emirates, US officials said.

Saudi and Emirati leaders both advocate a tough US approach against common foe Iran.

Pompeo described Saudi Arabia and the UAE as "two great allies in the challenge that Iran presents".

"We'll be talking with them about how to make sure that we are all strategically aligned and how we can build out a global coalition," Pompeo said.

He said the US sought a coalition "not only throughout the Gulf states but in Asia and in Europe that understands this challenge and that is prepared to push back against the world's largest state sponsor of terror".

But on Monday Russia, one of the world powers that negotiated the nuclear deal with Iran, denounced the planned new sanctions as "illegal".