The United Arab Emirates secretly attacked Iran in April after Iran launched a barrage of drone attacks against the Gulf nation in retaliation for U.S.-Israeli airstrikes.

Citing sources familiar with the matter, the Wall Street Journal reported on Monday that the UAE carried out military strikes on Iran, casting “the Gulf monarchy as an active combatant in a war in which it has been Iran’s biggest target”.

The strikes, which took place in early April, included an attack on a refinery in ‌Iran’s Lavan Island in the Persian Gulf.

According to the report, the UAE’s military is well-equipped with Western-made jet fighters and surveillance networks.

The UAE Embassy in Nigeria did not immediately return requests for comment on the report.

The attack, which killed Iran’s supreme leader Ali Khamenei and about 40 Iranian officials, escalated tensions in the Middle East as Iran launched retaliatory strikes at U.S. bases in the region while blocking the Strait of Hormuz.

In March, two different reports alleged that President Donald Trump’s decision to launch a military onslaught against Iran was influenced by intense lobbying by Saudi Crown Prince Mohammed bin Salman.

However, Saudi authorities denied claims that Mr Salman secretly lobbied the U.S. president to launch military strikes on Iran.