"(May) will acknowledge the steps taken recently by Saudi Arabia to address the crisis but stress the importance of full and unfettered humanitarian and commercial access, including through the ports," he said Tuesday.
"She will also reiterate how seriously we take allegations of violation against international humanitarian law and emphasise the need to ensure these are investigated swiftly and thoroughly."
Saudi crown prince lands in Egypt on first public trip
The spokesperson added the prime minister would "make clear that we urgently need to see progress on the political track... to end the conflict and humanitarian suffering in Yemen."
Britain is rolling out the red carpet for the crown prince's controversial three-day visit, which Downing Street hopes "will usher in a new era in bilateral relations" but is also expected to draw protests.
Salman will lunch Wednesday with the Queen at Buckingham Palace, while Prince Charles will host him at a dinner with Prince William among the guests.
The crown prince will jointly host with May the inaugural UK-Saudi strategic partnership council in No. 10, the prime minister's office and residence.
The summit, attended by ministers from both countries, will focus on support for reforms in Saudi Arabia, trade relations, defence and security, according to Downing Street.
"An important part of the visit will be exploring ways we can support Saudi to progress and intensify these reforms," May's spokesman said, noting the enacted or proposed lifting of bans on women in sports, going to cinemas and being able to drive in the kingdom.
Saudi crown prince heads West to woo allies, promote moderate Islam
Protest group Stop the War will hold a rally outside Downing Street at 5.00pm (1700 GMT) on Wednesday to denounce Saudi Arabia's "brutal and illegal bombing" in Yemen and London's support for the Middle Eastern regime.
Meanwhile NGO Save the Children will also protest the conflict by placing a life-size statue of a child near parliament "to draw attention to the violence that is being fuelled, in part, by British-made bombs".
Saudi Arabia's Foreign Minister defended his country's "just" war in
Yemen on the eve of the crown prince's visit, which follows a trip to Egypt earlier in the week and comes ahead of a visit to the United States later in March.
"They criticise us for a war in Yemen that we did not want, that was imposed on us," Adel Al-Jubeir told BBC radio.
"They criticise us for a war in Yemen that is a just war, that is supported by international law," he added.
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