The head of the Russian National Security Council, Nikolai Patrushev said on Tuesday that Iranian defenses downed a U.S. spy drone last week while the aircraft was in Iranian airspace.

Speaking at the opening of a meeting in Jerusalem with his U.S. and Israeli counterparts John Bolton and Meir Ben-Shabbat, Patrushev said Russia had intelligence information that the U.S. drone had been inside Tehran's airspace when it was shot down by Iranian defenses.

During his speech, Patrushev added that evidence provided by the U.S. allegedly implicating Iran in attacks on two oil tankers in the Gulf of Oman was "poor and unprofessional".

Earlier this month, an attack on ships in the Gulf of Hormuz -- blamed by the U.S. on Iran, a charge Tehran denies -- and Iran’s downing of a U.S. drone on Thursday further raised fears of conflict.

On Monday, the U.S. imposed sanctions on Iran's Supreme Leader Ayatollah Ali Khamenei, his office and eight senior commanders of Iran's elite Islamic Revolutionary Guard Corps.

The fresh sanctions came days after Iran on Thursday shot down a U.S. spy drone, which Tehran says violated its airspace while Washington maintains it had been flying over international waters above the Strait of Hormuz, an important shipping route.

Tensions have been rising between the U.S. and Iran since May 2018, when Washington unilaterally withdrew from a landmark 2015 nuclear deal between Tehran and the five permanent members of the UN Security Council plus Germany and the EU.

The U.S. has since embarked upon a diplomatic and economic campaign to put pressure on Iran in order to renegotiate the agreement, as well as other Iranian activities Washington considers to be "destabilizing".

As part of its campaign, the U.S. has re-imposed sanctions on exports of Iranian crude oil, which have nosedived the Iranian economy.