The United Kingdom has sold 500 cluster bombs to Saudi Arabia in the 1980s which the monarchy has used in its war against Yemen, an official report says.

According to a letter by British Defense Secretary Michael Fallon addressing conservative parliamentarian Philip Hollobone, Britain delivered 500 BL755 cluster bombs to Saudi Arabia under a government-to-government agreement signed in 1986.

Under the agreement, the final delivery was made in 1989.

“The fact so many British-made cluster bombs were sold and are now being used in Yemen is a stain on the UK's reputation worldwide,” Liberal Democrat shadow Foreign Secretary Tom Brake said.

“Michael Fallon has an urgent responsibility to address this shameful legacy, by suspending arms sales to the Saudi regime and putting pressure on it to stop using these horrific weapons.”

Saudi Arabia has waged a war against Yemen since March 2015. The Saudi aggression has killed more than 11,400 Yemenis so far.

The UK has been one of the main suppliers of weapons to Saudi Arabia for nearly 40 years.

The British government rejected calls, in November, by two parliamentary committees and human rights groups that urged a halt in selling weapons to Riyadh.

This is while on Monday, Amnesty International called for “an immediate suspension of all further weapons sales to Saudi Arabia.”