TOKYO (Kyodo) -- Prime Minister Shigeru Ishiba said Sunday that Japan is monitoring with "grave concern" the developments in the Middle East after the United States attacked Iranian nuclear facilities, though he refrained from expressing immediate support for the military action taken by its closest ally.

Speaking to reporters, Ishiba underscored the importance of de-escalating the situation while stressing that Iran's nuclear development must be "blocked."

Japan has traditionally maintained amicable ties with Iran even as its security alliance with the United States has remained strong. Stability in the Middle East is important for resource-scarce Japan, given its heavy dependence on the region for crude oil.

While no immediate impact on energy supplies has been confirmed, Ishiba said he has instructed officials to closely monitor the situation with urgency and take all necessary measures.

"We are gathering and analyzing information and closely monitoring developments with grave concern," Ishiba said.

Asked whether Japan backs the U.S. attacks, Ishiba said, "I will answer the question when appropriate," after holding discussions within the government on the matter.

The attacks on three key nuclear facilities have brought the United States into Israel's war against Iran, with President Donald Trump saying Saturday the airstrikes had "completely and totally obliterated" the facilities.

Another batch of evacuated Japanese nationals and their family members, totaling 21, arrived by bus in Azerbaijan from Iran on Sunday, with none of them having any health issues, according to the Foreign Ministry.

Their departure came after 87 Japanese nationals and their family members left Iran and Israel on Thursday.

Around 200 Japanese nationals remain in Iran, while around 1,000 are still in Israel, according to the ministry.

Israel and Iran have been engaged in open warfare since the former attacked Iranian nuclear facilities and military targets on June 13, claiming that Iran was close to obtaining a nuclear weapon despite its denials.