Japanese Prime Minister Shinzo Abe is in Tehran for talks, hoping they could ease tensions between Iran and the US.
He is the first Japanese prime minister to visit Iran in four decades and is due to meet the country’s leaders.
Iran has been angered by sweeping US sanctions imposed after President Trump abandoned a deal in which the Iranians agreed to curb their nuclear programme.
Observers doubt what Mr Abe can achieve, and see it as an image boost for him before elections.
Iranian state television carried live pictures of Mr Abe’s arrival. He was expected to go straight into talks with President Hassan Rouhani and to meet Supreme Leader Ayatollah Ali Khamenei on Thursday.
Officially, Japan and Iran are marking the 90th anniversary of their diplomatic relationship this year.
Much more significant is that the trip comes shortly after US President Donald Trump made a state visit to Japan, a key US ally.
US relations with Iran nosedived over Washington’s withdrawal from the 2015 nuclear deal over Iran’s nuclear programme.
Tensions escalated further when the US sent an aircraft carrier to the region, raising fears of a military confrontation.
There are hopes that Mr Abe might be able to engage in some diplomacy between the two sides, dialing down tensions and getting them to talk to each other.
Just one day before heading off, the Japanese prime minister spoke to Mr Trump on the phone and exchanged views on Iran, a spokesperson for Mr Abe told reporters on Tuesday.
Essentially, in 2015, Iran agreed to limit its nuclear programme in return for sanctions being lifted.
The deal was done under the Obama administration though, and Mr Trump withdrew from it last year.
The US reinstated unilateral sanctions while other signatories to the 2015 deal – like the European Union (EU), Russia and China – still hope to keep the agreement alive.
In retaliation for sanctions reinstated by the US, Iran last month announced it would suspend some commitments.
On Tuesday, the International Atomic Energy Agency (IAEA) said Iran was increasing its production of enriched uranium, though it’s not clear when it will reach a limit set under the 2015 deal.
Tokyo has never been part of the Iran agreement but that does not mean it isn’t affected. –BBC