Updated

Saudi Arabia's crown prince was being greeted Wednesday in Britain by Queen Elizabeth II — and met by protesters against the war in Yemen.

Theresa May's office said the prime minister will "raise deep concerns at the humanitarian situation" in Yemen when she meets Mohammed bin Salman at her office at 10 Downing Street. Human rights campaigners rallied near Parliament and said they would protest later outside the gates of Downing St.

A Saudi-led coalition has been battling Iran-allied rebels in Yemen since 2015 in a war that has killed more than 10,000 people and driven the Arab world's poorest country to the brink of famine. The kingdom faces wide international criticism for its airstrikes killing civilians and striking markets, hospitals and other civilian targets.

Critics say Britain has been slow to condemn abuses by Saudi Arabia, a key regional ally and major purchaser of U.K.-made weapons.

Britain is rolling out the red carpet for the 32-year-old crown prince, who will have lunch Wednesday with the queen at Buckingham Palace and dine later with Prince Charles and Prince William.

The Saudi royal has shaken up his deeply conservative country since he became heir apparent to King Salman last year.

The crown prince swiftly consolidated power by sidelining rivals and stepped up Saudi Arabia's rivalry with Iran. He has also has pushed through a number of dramatic social reforms including allowing women to drive and lifting a ban on movie theaters.

Critics say the modernization measures mask continuing rights abuses. Human rights charity Reprieve says the number of executions in Saudi Arabia has doubled since the crown prince took charge.

The three-day visit is also due to include lunch with May at the prime minister's rural retreat, Chequers, and talks with Defense Secretary Gavin Williamson.