“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 on Saturday after returning from a trip to Malaysia and Japan.
“Japan is sending a surveillance vessel but not to the Gulf and the Strait of Hormuz,” he said.
Subsequent US sanctions, which block Iran from selling crude oil abroad, have crippled its economy, prompting Tehran to gradually reduce its commitment to the nuclear deal.
Washington proposed the naval mission after several attacks in May and June on international merchant vessels, including Saudi tankers, in Gulf waters which the US 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.
Rouhani said his discussions in Japan included ways of “breaking” the US sanctions.
“On breaking the sanctions, the Japanese had a new proposal and we also had a new proposal and we discussed this and it was decided to continue the consultations between the two countries on this issue,” Rouhani said, without giving details.
Following his meeting with Japanese Prime Minister Shinzo Abe, Rouhani tweeted on Friday: “I welcome any effort that could boost economic exchanges, especially in the energy sector, and increase oil exports.”
A Japanese official who gave a briefing to reporters said crude oil purchases were not discussed at the summit meeting. Japan was a leading buyer of Iranian oil for decades before the US-led sanctions.
Japan, a US ally maintaining friendly ties with Iran, is looking to launch its own naval 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 a patrol aircraft for gathering information in the Gulf region, which has been the source of nearly 90 percent of Japan’s crude oil imports.
A European operation to ensure safe shipping in the Gulf will get underway next month when a French warship starts patrolling there. The French government has pushed for a European security alternative after ruling out taking part in the US-led mission.