Qatar is trying to "defuse escalating tensions" across the Persian Gulf, Al Jazeera reports amid allegations of oil tanker sabotage, a drone attack by Yemen's Iranian-allied rebels and deployment of US warships and bombers to the region.
Iran is showing "maximum restraint" despite the US withdrawal from an international nuclear deal, the country's foreign minister said on Thursday.
"The escalation by the United States is unacceptable," Mohammad Javad Zarif said in Tokyo where he is holding talks with Japanese officials.
"We exercise maximum restraint... in spite of the fact that the United States withdrew from JCPOA last May," he added, referring to the 2015 nuclear deal known as the Joint Comprehensive Plan of Action which has steadily unravelled amid rising tensions in the Mideast.
Recent days have seen allegations of sabotage attacks targeting oil tankers off the coast of the United Arab Emirates, a drone attack on a Saudi oil pipeline claimed by Yemen's Iran-allied Houthi rebels, a retaliatory attack by the kingdom and its allies on Yemen and the dispatch of US warships and bombers to the region.
These followed Iran's recent decision to stop complying partially with JCPOA.
Doha has gotten involved in efforts to "defuse escalating tensions" across the Persian Gulf, Qatar-funded news broadcaster Al Jazeera said.
Al Jazeera cited an anonymous official on Wednesday night as saying that Qatari Foreign Minister Sheikh Mohammed bin Abdulrahman Al Thani had travelled to Tehran in recent days to speak with Zarif.
Al Jazeera said the US was aware of the trip in advance, but did not elaborate further.
FlightRadar24.com, a flight-tracking website, showed a Qatari government airplane landed in Tehran on Saturday.
Qatar hosts the forward headquarters of the US military's Central Command at its vast Al Udeid Air Base. Several of the B-52 bombers ordered by the White House to the region amid the latest escalation between Washington and Tehran are stationed there.
Qatar has grown closer to Iran diplomatically amid it begin boycotted by four Arab nations over a political dispute.
The root of all problems
At the root of all this appears to be President Donald Trump's decision a year ago to pull the US from Iran's nuclear deal with world powers, embarking on a maximalist sanctions campaign against Tehran.
In response, Iran's supreme leader issued a veiled threat on Tuesday, saying it wouldn't be difficult for the Islamic Republic to enrich uranium to weapons-grade levels.
He also said that while his country would not negotiate with the United States, Iran is not seeking war.
On Wednesday, the US Department of State ordered all nonessential government staff to leave Iraq.
Germany and the Netherlands both suspended their military assistance programmes in the country in the latest sign of tensions. Germany, however, added on its own, it has not seen threats from Iran and training might resume shortly.
The movement of diplomatic personnel is often done in times of conflict, but what is driving the decisions from the White House remains unclear.
Iraq is home to powerful pro-Iranian militias, while also hosting more than 5,000 US troops. The Central Command said its troops were on high alert, without elaborating.
Last week, US officials said they had detected signs of Iranian preparations for potential attacks on US forces and interests in the Middle East, but Washington has not spelled out that threat.
Iran's nuclear compliance
In Thursday's visit to Tokyo Zarif told his Japanese counterpart Taro Kono that his country's response to the US actions is within the nuclear deal and Iran's rights.
Iran's recently threatened to resume higher enrichment in 60 days if no new nuclear deal is in place, beyond the level permitted by the current deal.
Kono expressed concern over the rising tension in the Middle East, and urged Zarif to use restraint and keep implementing the nuclear agreement.
Under the current deal, Iran is permitted to enrich uranium upto 3.67 percent.
Iranian officials have said that they could reach 20 percent enrichment within four days.
Though Iran maintains its nuclear programme is for peaceful purposes, scientists say the time needed to reach the 90 percent threshold for weapons-grade uranium is halved once uranium is enriched to around 20 percent.