Iranian President Hassan Rouhani on Saturday welcomed Japan's decision not to join a US-led naval mission in the Gulf, in remarks carried by state television.
Friction between Tehran and Washington has increased since last year when US President Donald Trump pulled the United States out of Iran's 2015 nuclear deal with six nations and re-imposed sanctions on the country, crippling its economy.
Washington proposed the naval mission after several attacks took place in May and June on international merchant vessels, including Saudi tankers, in Gulf waters which the United States blamed on Iran. Tehran denies the accusations.
In July, Iranian forces seized a British tanker in the Gulf after British marines captured an Iranian vessel in the Strait of Gibraltar. Both ships were later released.
"Japan has announced it will not take part in the Americans' plans for security in the (Gulf) region ... which is something we welcome," Rouhani said on state TV after returning from a visit to Malaysia and Japan.
"Japan is sending a surveillance vessel but not to the Gulf and the Strait of Hormuz," he added.
Japan, a US ally maintaining friendly ties with Iran, is looking to launch its own operation rather than joining the US-led mission to protect shipping in the region.
The planned Japanese operation is set to cover high seas in the Gulf of Oman, the northern Arabian Sea and the Gulf of Aden, but not the Strait of Hormuz.
According to a draft plan approved by parties in the ruling coalition, Japan will deploy a destroyer and P-3C patrol aircraft for gathering information in the Gulf region - the source of nearly 90 percent of Japan's crude oil imports.