Iran has warned Washington on the activation of terrorist sleeper cells in the United States few days before the U.S. attack, NBC News reported on Monday, citing unnamed sources.

U.S. President Donald Trump had reportedly received a communiqu? last week in which Iran threatened to activate such cells in the U.S. if Washington made a decision to attack Iran.

The sources said that the U.S. leader got the message through an intermediary at the G7 summit in Canada last week, the broadcaster reported.

The U.S. struck three Iranian nuclear sites in Natanz, Fordow and Isfahan in the early hours of Sunday.

Trump said after the attack that Tehran ?must now agree to end this war?? or face far more serious consequences.

The U.S. strikes drew widespread international condemnation.

UN Secretary-General Antonio Guterres described them as a dangerous escalation and a threat to global peace.

Russia strongly denounced the attacks, calling them gross violations of international law, the UN Charter, and UN Security Council resolutions urged the International Atomic Energy Agency (IAEA) to respond impartially.

Israel launched a large-scale operation against Iran, Rising Lion, in the early hours of June 13, accusing it of implementing a secret military nuclear programme.

The Israeli air force carried out several waves of attacks across Iran, including in Tehran, killing a few senior Iranian military officials, as well as several nuclear scientists, a few nuclear sites, including Natanz and Fordow, were also hit.

Iran?s Supreme Leader Ayatollah Ali Khamenei called the attack a crime and threatened Israel with a ?bitter and terrible fate.?

Tehran retaliated by launching Operation True Promise 3 on June 13 evening, which hit military targets inside Israel.

Iran denies the military dimension of its nuclear programme.

The International Atomic Energy Agency has not seen concrete evidence that Iran has an active nuclear weapons program, Director General Rafael Grossi said on June 18.

U.S. intelligence assessments reached a similar conclusion that Iran was not actively pursuing nuclear weapons, CNN reported on June 17, citing people familiar with the issue.

A former UK Ambassador to Uzbekistan, human rights activist Craig Murray told RIA Novosti that Iran was ?extraordinarily responsible and patient? over the last several years, in spite of Israel?s actions. (RIA/NAN)

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