Iranian President Hassan Rouhani (L) shakes hands with Japanese Prime Minister Shinzo Abe (R) before a meeting at the prime minister's office in Tokyo on December 20, 2019.Photo: AFP

President Hassan Rouhani became the first Iranian head of state to visit Japan in two decades on Friday, as Tokyo seeks to mediate between Tehran and Washington amid spiraling nuclear tensions.

The two men inspected a guard of honor at Japanese Prime Minister Shinzo Abe's central Tokyo office before summit talks and a dinner. They are not scheduled to brief reporters after the talks. 

The trip comes after deadly protests last month over petroleum price hikes in Iran, as Washington-imposed sanctions over its nuclear program hit the Iranian economy.

The US re-imposed crippling sanctions on Iran in 2018 after withdrawing from an international deal aimed at tackling the Islamic Republic's nuclear program.

Iranian government spokesman Ali Rabiei has played down the mediation aspect of the trip, saying the visit to Tokyo had "nothing to do with issues such as negotiations with America."

But he said that "our Japanese friends usually convey messages or initiatives, which we welcome... and seriously examine."

As a key US ally that also maintains close diplomatic and economic ties with Iran, Abe has tried to build bridges between the two rival powers. Last week, Abe said he would strive "as much as possible to ease tensions" in the Middle East, noting Japan's alliance with Washington and "favorable relations" with Tehran.

Abe travelled to Tehran in June to try to ease tension between the US and Iran in the Gulf.

Japan was formerly a major buyer of Iranian crude but stopped purchases to comply with the US sanctions.

The prime minister was expected to explain to Rouhani Tokyo's plans to send two Self Defense Forces ships to the Gulf of Oman to protect shipping there.

"At the Japan-Iran summit today we will explain Japan's policy. This kind of policy is aimed at securing Japanese vessels' safety," said government spokesman Yoshihide Suga, adding that 90 percent of Japan's crude oil imports come from the region.

Rouhani comes to Japan from Kuala Lumpur where he called on Muslim countries at a summit to band together to fight US "economic terrorism."

The US sanctions "are having a serious impact on every aspect of Iran," Hitoshi Suzuki, a Middle East scholar at the Institute of Developing Economies (IDE-JETRO), told AFP.