Iranian President Hassan Rohani, on a visit to Japan, has asked for Tokyo's help to salvage a 2015 landmark nuclear deal.
Tensions between Iran and the United States have spiraled after U.S. President Donald Trump last year pulled Washington out of the nuclear deal between Tehran and world powers.
Washington has since reimposed crippling sanctions on Iran in an effort to tackle the country's nuclear and missile program, while Tehran has gradually reduced some of its commitments under the agreement.
Rohani is the first Iranian leader to visit the East Asian country in nearly two decades. His trip comes after Shinzo Abe became in June the first Japanese prime minister to travel to Iran in more than 40 years.
Japan, a U.S. ally that maintains friendly ties with Tehran, has been "making diplomatic efforts, in cooperation with relevant countries including the United States and Iran, in order to ease the tensions and stabilize the situation in the Middle East," Japan's Foreign Ministry said in a statement.
Iranian government spokesman Ali Rabiei has acknowledged that Japanese officials "usually convey messages or initiatives, which we welcome...and seriously examine."
But he said Rohani’s trip to Tokyo had "nothing to do with issues such as negotiations with America."
Rohani renewed his condemnation of the United States for pulling out of the nuclear deal.
"The nuclear deal is an extremely important agreement for Iran. That's why we strongly condemn the United States' one-sided and irrational withdrawal," he said during talks with Abe on December 20.
At the start of the talks, Abe said Japan would do what it can to ensure stability in the Middle East, the source of more than 80 percent of its oil.
"I'm highly concerned about tensions running high in the Middle East," Abe told Rohani.
He also asked Rohani to stick to the country's commitments to the nuclear accord, while the Iranian president asked the Japanese leader to work with other countries to help keep the pact in place.
Abe also briefed Rohani on Tokyo's plan to send naval forces to the Middle East to protect Japanese vessels, a Japanese official said.
In June, a Japanese-operated tanker was attacked in the Gulf of Oman, the northern part of the Arabian Sea.
Washington has accused Iran of being responsible and urged Japan to join a U.S.-led coalition in the Strait of Hormuz to help ensure the safe navigation of ships on the world's most important oil transit route.
Japan's government is expected to soon finalize a plan to dispatch its navy to the Middle East.
Iranian officials have rejected the presence of foreign forces in the region, saying it would create insecurity for oil and shipping.