Prime Minister Mustafa al-Kadhemi of Iraq met Ayatollah Ali Khamenei in the Iranian capital during his first trip abroad since taking office.

"Iran will not interfere in Iraq's relations with America but expects Iraqi friends to know America and realise that their presence in any country causes corruption, ruin and destruction," the Iranian leader said, according to his official website.

"The Islamic republic expects... (the Iraqi) parliament's decision to expel the Americans to be adhered to since their presence is a cause of insecurity."

Khamenei pointed to the US killing of Iran's top general Qasem Soleimani in a January drone strike in Baghdad, after which parliament voted to expel US troops.

"They killed your guest in your house and blatantly confessed to it."

Iran "will never forget this and will certainly deal a reciprocal blow to the Americans", Khamenei said.

Iran retaliated for Soleimani's death days after by firing a volley of missiles at US troops stationed in Iraq, but US President Donald Trump opted against responding militarily.

While the attack on the western Iraqi base of Ain al-Asad left no US soldiers dead, dozens suffered brain trauma.

According to Khamenei, Iran was opposed to "whatever may weaken the Iraqi government" in contrast to the US, which he said did not want "an independent, strong Iraqi government elected by popular vote".

- Tug-of-war -

Kadhemi had been scheduled to visit Iran's regional rival Saudi Arabia as his first trip abroad, then quickly follow it up with a trip to Tehran, in a carefully calibrated balancing act.

The Saudi leg was postponed after King Salman was hospitalised on Monday.

Baghdad has often found itself caught in the tug-of-war between Riyadh, Tehran and Washington, which Kadhemi is also set to visit within weeks.

Kadhemi rose to the premiership in May after serving as head of Iraq's National Intelligence Service for nearly four years.

He formed close ties to Tehran, Washington and Riyadh during that time, prompting speculation he could serve as a rare mediator between the capitals.

His trip to Tehran comes after he received Iran's top diplomat Mohammad Javad Zarif in Baghdad on Sunday.

Relations between the two countries were not always close -- they fought a bloody war from 1980 to 1988.

Tehran's influence in Baghdad grew after the 2003 US-led invasion of Iraq toppled the government of Saddam Hussein.

Iran is now said to have significant leverage over many of Iraq's Shiite political groups.

- $20 billion trade goal -

Iraq's delegation includes the ministers of foreign affairs, finance, health and planning, as well as Kadhemi's national security adviser, some of whom also met their Iranian counterparts.

Kadhemi also held talks with President Hassan Rouhani to discuss closer trade ties, fighting the novel coronavirus and efforts to ensure regional stability, state television said.

"The two governments' will is to expand bilateral trade ties to $20 billion," Rouhani said after their hour-long meeting.

Iraq is one of Iran's main markets for non-oil exports but trade has dipped as the COVID-19 pandemic forced temporary border closures.

Rouhani said Iran was ready to "stand with Iraq for the stability and security of Iraq and the region".

He hailed as "heroes" Soleimani and an Iraqi commander killed alongside him in the US drone strike near Baghdad airport.

"I deem it necessary to honour the two heroes of the fight against terrorism, martyrs General Qasem Soleimani and Abu Mahdi al-Muhandis," he said.

The Iranian president also pledged to help Baghdad fight coronavirus.

Iran says COVID-19 has claimed more than 14,600 lives and infected 278,800 in the country, while has reported close to 4,000 virus deaths and 97,000 cases.