Iran's Foreign Minister Mohammad Javad Zarif on Thursday accused outgoing US President Donald Trump of aiming to fabricate a "pretext for war" as tensions mount between the two countries.

His remarks come ahead of the first anniversary of the US killing of top Iranian military commander Qasem Soleimani in a drone strike in Baghdad on January 3.

US aircraft carrier USS Nimitz has been patrolling Gulf waters since late November and two American B-52 bombers recently overflew the region.

"Instead of fighting (the novel coronavirus) in US, @realDonaldTrump & cohorts waste billions to fly B52s & send armadas to OUR region," Zarif wrote on Twitter.

"Intelligence from Iraq indicate plot to FABRICATE pretext for war," he added.

Trump ordered a drone strike on January 3 this year to kill Soleimani near Baghdad's international airport.

Days later, Iran launched a volley of missiles at Iraqi bases housing US and other coalition troops, with Trump refraining from any further military response.

"Iran doesn't seek war but will OPENLY & DIRECTLY defend its people, security & vital interests," Zarif said.

Trump said last week said he would hold "Iran responsible" for any fatal attack on Americans in Iraq after accusing Tehran of being behind a rocket strike on the US embassy in Baghdad on December 20.

Zarif at the time warned the US president against any "adventurism" before leaving the White House on January 20, and said "putting your own citizens at risk abroad won't divert attention from catastrophic failures at home".

The US embassy in Iraq and other foreign military and diplomatic sites have been targeted by dozens of rockets and roadside bomb attacks since later 2019.

Trump unilaterally withdrew the US from a landmark nuclear deal with Iran and world powers in 2018 and launched a "maximum pressure" campaign against Tehran, reimposing and reinforcing crippling sanctions.

The two countries have twice come to the brink of war since June 2019, especially following the killing of Soleimani.