Iran's President Ebrahim Raisi called on Japan to release Iranian funds frozen in the country because of US sanctions, Iranian media reported after the president met on Sunday with the visiting Japanese foreign minister.

Iran has been unable to obtain tens of billions of dollars of its assets mainly from exports of oil and gas in foreign banks, including $3 billion of its funds in Japan, due to US sanctions on its banking and energy sectors.

"The improvement of ties with Japan is of great importance for Iran ... Any delay in unblocking Iranian assets in Japanese banks is not justified," Raisi said in his meeting with Toshimitsu Motegi, who arrived in Tehran late on Sunday for a two-day visit.

In a tweet earlier on Sunday, outgoing Iranian Foreign Minister Mohammad-Javad Zarif said he had discussed strengthening "bilateral relations, how to resuscitate the JCPOA and the catastrophic US-engineered situation in Afghanistan", with his visiting Japanese counterpart Toshimitsu Motegi.

Motegi who arrived on Saturday is on a Middle East tour that has also taken him to Israel. He is scheduled to meet with Iran's new President Ebrahim Raisi and former deputy foreign minister Hossein Amir Abdollahian who Raisi has proposed to succeed Zarif.

This is the first time in about two years that the Japanese foreign minister is visiting Tehran and the first high-ranking foreign official meeting with Raisi since he took office earlier this month. Observers believe the Japanese foreign minister may be in Tehran to mediate between Iran and the United States over the revival of the 2015 nuclear agreement, the Joint Comprehensive Plan of Action (JCPOA). Talks in Vienna were paused by Iran in June and are awaiting for Raisi's foreign policy team to take over from Zarif and his team.

In a note published in Iran newspaper before his arrival in Tehran, Motegi said he had decided to visit Iran and meet with Raisi "at the earliest convenience" to "strengthen bilateral relations" and stressed that peace and stability in the Middle East is crucial to Japan which procures 90 percent of its crude oil imports from the region.

Japan was one of the major buyers of Iran's crude oil before Donald Trump withdrew from the JCPOA in 2018 and omposed oil export sanctions on Tehran. The country has maintained friendly relations with Iran over the years despite being a US ally.

In June 2019, then Prime Minister of Japan Shinzo Abe visited Tehran in a bid to broker a dialogue between Tehran and Washington. During the visit, the first by a Japanese prime minister in over four decades, Abe met with Iran's Supreme Leader Ali Khamenei and former President Hassan Rouhani. Abe was reportedly carrying a message from Trump but Khamenei rejected Abe's offer of mediation and said he did not consider Trump as a person "worth exchanging any messages with" and had no response for him then or in the future.

On the same day that Abe was meeting Khamenei, two tankers one of which was operated by a Japanese company were attacked near the Strait of Hormuz, allegedly with limpet mines. The US, Britain and Saudi Arabia blamed Iran for the attack but Iran denied the accusations.

In his note Motegi also highlighted his personal support for Japan's decision to donate 2.9 million doses of Covid-19 vaccines – AstraZeneca produced in Japan – to Iran in July under the international Covax mechanism. Many Iranians who have been anxiously waiting for vaccines to arrive welcomed Japan's donation on social media. Iran's vaccination program has been very slow due to Khamenei's ban in January on US and UK-produced vaccines. Russian and Chinese vaccine suppliers' also failed to make promised deliveries, and production of Iranian-made CovIran Barakat is hugely lagging behind targets. The country is currently gripped by a health crisis with Covid deaths rising to unprecedented figures in recent days.