Russian Foreign Minister Sergei Lavrov said on Tuesday that Moscow had still seen no evidence that Iran was developing nuclear weapons as the U.S. and Israel pursue their attack.
U.S. President Donald Trump has offered various reasons for going to war with Iran. On Monday, in his most extensive public comments so far, he said he had ordered the attack to thwart Tehran's nuclear and ballistic missile programmes.
Lavrov told Brunei's foreign minister during talks in Moscow: "We still see no evidence that Iran was developing nuclear weapons, which was the main, if not the only, justification for the war."
He said the consequences of the attack on Iran were being felt throughout the region, and that Arab countries were bearing economic costs and suffering casualties.
He reiterated Russia's call for an immediate cessation of hostilities by all parties:
"As an unconditional first step, we must do everything possible to stop any actions that result in civilian casualties."
He pointed to the reported bombing of a school in Iran.
Iranian state media have accused Israel and the U.S. of a strike on a girls' primary school in the southern Iranian town that Tehran said had killed more than 160 people.
U.S. Secretary of State Marco Rubio said U.S. forces would not deliberately attack a school.
