The US State Department on Wednesday ordered all non-emergency staff to leave its embassy in Baghdad and consulate in Erbil, as tensions mount between the United States and Iraq's neighbour Iran.

Washington has ramped up pressure on Tehran in recent days, accusing Tehran of planning "imminent" attacks in the region, and bolstering the American military presence in the Gulf. However, US Secretary of State Michael Pompeo has claimed that his country is not seeking war with Iran, despite a spike in tensions that has seen the Pentagon dispatch nuclear-capable bombers to the region.

"Normal visa services at both posts will be temporarily suspended," the US State Department said, recommending those affected depart as soon as possible. It was unclear how many staff would leave.

A State Department spokesman said the decision to withdraw non-emergency staff was based on a security assessment, but would not give details on how many personnel were leaving.

"Ensuring the safety of US government personnel and citizens is our highest priority and we are confident in the Iraqi security services' (ability) to protect us," he said. "But this threat is serious and we want to reduce the risk of harm."