British Prime Minister Theresa May is to visit Saudi Arabia for talks on Wednesday with its assertive crown prince over the kingdom-led war in Yemen, the second European leader to specifically seek him out as he amasses power.

May's visit is expected to include her asking Crown Prince Mohammed bin Salman to allow humanitarian aid through Yemen's port of Hodeida, which is held by the Shia rebels being targeted in the Saudi-led war.

A UN-chartered aid vessel docked at Hodeida on Tuesday.

“We are very clear that we want to see full humanitarian and commercial access through the port of Hodeida,” May said Tuesday.

“Obviously that is an issue I will be raising when I am in Saudi Arabia.”

Saudi Arabia closed off Yemen's seaports and airports over a November 4 rebel ballistic-missile launch that targeted the Saudi capital of Riyadh. The kingdom said it intercepted the missile, the deepest yet to penetrate the country.

Under intense international pressure, Saudi Arabia later promised it would reopen the ports for humanitarian aid.

The Saudi-led coalition began its war in Yemen in March 2015 on behalf of Yemen's internationally recognised government against the Houthis rebels and their allies.

The conflict has pushed the Arab world's poorest country to the brink of famine. The war has killed over 10,000 civilians, displaced 3 million people and left much of the infrastructure in ruins.

May has faced increasingly calls to stop British arms sales to Saudi Arabia amid the conflict, which has seen kingdom-led airstrikes kill hundreds of civilians. Britain has licensed $4.4 billion worth of arms sales to Saudi Arabia since the war began.

May's visit seeking out Crown Prince Mohammed comes as the 32-year-old son of King Salman now appears to hold the levers of power in Saudi Arabia. French President Emmanuel Macron made a surprise visit to the kingdom earlier this month as well, to see the young royal.

In recent weeks, the crown prince led what the kingdom described as an anti-corruption campaign, arresting prominent princes, business leaders, military officials and others. He also was the architect of the kingdom's war in Yemen, which has been at a stalemate for months.

May also will visit Jordan and meet with King Abdullah II on her trip.