Activists in the UK are calling on British Prime Minister Theresa May to withdraw an invitation to Saudi Crown Prince Mohammed Bin Salman, who is expected to visit within a few weeks.

Groups including the Stop the War coalition, the Campaign Against Arms Trade, and the Arab Human Rights Organisation, published an open letter on Friday accusing the heir to the Saudi throne of overseeing the war on Yemen and deepening a humanitarian crisis there.

"[Mohammed bin Salman] is the second most senior member of the Saudi regime, which has one of the worst human rights records in the world," the statement read.

"Torture, arbitrary detention, and other appalling abuses are widely documented."

Stephen Bell, one of the activists leading the campaign to stop the visit, told Al Jazeera the UK should not "lay out the red carpet" for Mohammed Bin Salman, who is known as MBS.

"Up to 11 million Yemeni children are at risk either from the war or cholera, famine caused by the blockade of the country and the destruction of infrastructure," he said.

"All this means it's not suitable to invite someone who holds prime responsibility for the continuation of the war."

Since the Saudi-led military intervention started in Yemen in March 2015, the Arab world's poorest country has found itself on the brink of a devastating humanitarian crisis, with the UN warning of widespread famine and spread of disease.

More than eight million people do not have adequate access to food and more than a million have contracted cholera.

UK support

British arms companies are some of the biggest suppliers of weapons to Saudi Arabia, and the British government has approved billions of pounds in export licenses over the past three years.

Rights groups have repeatedly condemned the Saudi-lead coalition over civilian casualties in Yemen, but the UK has yet to take any punitive measures against Riyadh.

British officials say they are monitoring the use of UK-manufactured weapons by Saudi Arabia to "ensure" they are used appropriately.

The conflict between the Saudi coalition and Houthi rebel fighters has left more than 10,000 people dead and devastated much of the country's infrastructure.