The visit by the prince, the kingdom’s de facto ruler, to the summit of industrialised nations is fraught with controversy over the killing of Saudi journalist Khashoggi in the Saudi consulate in Istanbul in October.

The killing of the Washington Post columnist, a critic of the crown prince, has strained Saudi Arabia’s ties with the West and battered Prince Mohammed’s image abroad. Saudi Arabia has said he had no prior knowledge of the murder.

“I am intending to speak with the crown prince of Saudi Arabia. The message that I give will be very clear … on this issue of Jamal Khashoggi but also on the issue of Yemen,” she told reporters on the flight to Buenos Aires.

“We want to see a full and transparent investigation in relation to what happened and obviously those responsible being held to account,” she said on Khashoggi’s killing.

Western nations are calling for an end to the Saudi-led military campaign in neighbouring Yemen, which was launched by Prince Mohammed, as a humanitarian crisis there worsens.

“On the issue of Yemen, we continue to be deeply concerned about the humanitarian situation,” May said. “The long term solution for the Yemen is a political situation and we will be encouraging all parties actually to look for that and work for that.”