David Cameron has arrived in Saudi Arabia on his first official as prime minister - against reports of the death of an anti-government activist.

Activists have reported the death of at least one person, 22-year-old Issam Mohamed, and three injured in a crackdown by security forces on Shia protesters in Saudi Arabia's Qatif region.

The claims surfaced as Cameron met King Abdullah and Crown Prince Nayef in Riyadh in the hope of "broadening and deepening" the UK-Saudi relationship, said No 10.

Saudi Arabia is one of the UK's largest trade partners in the Middle East and bilateral trade has increased by over 160% to £2.2bn over the last five years.

"Saudi Arabia is our largest trading partner in the Middle East but it also has unique influence in the region and in the Islamic world," a Cameron spokesman said.

"It has been influential in the work of the Arab League in putting pressure on the repressive regime of [Syrian] President Assad.

"People who think we shouldn't be friends with - or our prime minister shouldn't be visiting - a country that is such an important ally and such an important force in the world would be advocating a head-in-the-sand policy, and that is not in our national interest." the spokesman told BBC Radio 4's World at One.

The meeting has been criticised as it is expected to touch on the arms trade between the two countries.

In December Saudi Arabia signed a $29bn arms deal with the US.