TOKYO (AFP, REUTERS, BLOOMBERG) - Iran's Foreign Minister said on Thursday (May 16) there is "no possibility" of negotiations with the United States to reduce spiralling tensions, Japan's Kyodo news agency reported.

"No, there is no possibility for negotiations," the news agency cited Mr Mohammad Javad Zarif as telling reporters in Tokyo, where he is meeting with Japanese officials.

Kyodo said the comment was in response to a question on whether he would be open to bilateral talks with Washington aimed at easing tensions.

It did not immediately carry additional comments from Mr Zarif, but public broadcaster NHK also quoted the Foreign Minister as describing US pressure on Iran as an "act of suicide".

Mr Zarif also reportedly dismissed US President Donald Trump's assertion in a tweet that Iran would soon seek negotiations.

"I don't know why President Trump is confident, but it's totally wrong," NHK quoted Mr Zarif as saying.

The quotes on NHK were published in Japanese, and it was not immediately clear whether they were translated from English or Farsi.

Washington withdrew a year ago from a nuclear deal with Teheran and re-imposed sanctions, prompting a deterioration in relations.

But the crisis has deepened in recent weeks, with the US deploying an aircraft carrier strike group and B-52 bombers to the Gulf over alleged threats from Iran.

The US on Wednesday withdrew staff from its embassy in Iraq, out of apparent concern about threats from Iran, with US sources saying they believe Iran encouraged recent attacks on oil tankers.

An attack on four oil tankers in the Gulf on Sunday, for which no one has claimed responsibility, and Saudi Arabia's announcement on Tuesday that armed drones had hit two of its oil pumping stations have compounded the worries about war.

British Foreign Secretary Jeremy Hunt on Thursday said he shared the same assessment as the US of the heightened threat posed by Iran. His statement came as the UK raised the threat level for its armed forces and diplomats in Iraq, citing an increased security risk from Iran, according to two people familiar with the matter.

The top Iranian diplomat, who met with Japan's Prime Minister Shinzo Abe on Thursday, earlier accused Washington of an "unacceptable" escalation in tensions, and said Teheran was showing "maximum restraint".

Iran is exercising "maximum restraint in spite of the fact the United States withdrew from (the) JCPOA last May", Mr Zarif said at the start of his meeting with Japanese Foreign Minister Taro Kono. He was referring to the Joint Comprehensive Plan of Action signed in 2015 by the US, Iran and other countries, under which Teheran curbed its uranium enrichment capacity and won sanctions relief in return.

Mr Zarif said Iran is committed to its obligations under an international nuclear deal despite the US withdrawal from the landmark agreement. He also called the reimposition of US sanctions "unacceptable".

"We believe that escalation by the United States is unacceptable and uncalled for," Mr Zarif told Mr Kono in front of reporters, before they met privately.

"I'm concerned that the situation in the Middle East is becoming very tense," Prime Minister Shinzo Abe told Mr Zarif in a later meeting.

Mr Kono said it was essential to maintain the nuclear agreement and urged Iran to keep implementing it, echoing other countries.

A US government source on Wednesday said American security experts believe Iran gave its "blessing" to attacks on two Saudi crude oil tankers, a UAE-flagged fuel bunker barge and a Norwegian-registered oil products tanker off Fujeirah near the Strait of Hormuz.

US Secretary of State Mike Pompeo made a surprise visit to Baghdad last week after US intelligence showed Iran-backed Shi'ite militias positioning rockets near bases housing American forces, according to two Iraqi security sources.

Helicopters took off throughout Wednesday from the US embassy compound near the Tigris River in Baghdad, carrying non-emergency employees out, said an Iraqi source and a diplomatic source inside Baghdad's fortified Green Zone.

Iran has described the US moves as "psychological warfare", while its Foreign Ministry said the tanker attacks were "worrisome and dreadful", and called for an investigation.

Nevertheless, Iran has relaxed restrictions on its nuclear programme and threatened action that could breach the nuclear deal, although the initial moves do not appear to violate the agreement.