When US President Donald Trump visited Riyadh last year he boasted that the desert kingdom would spend $110 billion on US equipment and the howitzer contract is one more step towards that goal.

Saudi Arabia's de facto ruler, Crown Prince Mohammed Bin Salman, is coming to the end of a three-week US tour that has been dotted with similar signs of his close ties with Trump's Washington.

Saudi Arabia has led a large-scale but so far unsuccessful Arab intervention in Yemen's civil war and has imposed a diplomatic and trade embargo on a fellow US ally in the Gulf, Qatar.

Recently, the crown prince detained Lebanon's Prime Minister Saad Hariri and tried to force him to resign.

Nevertheless, in announcing the weapons package, the US State Department described the kingdom as "a leading contributor of political stability and economic progress in the Middle East."

According to the statement, the latest deal will see Saudi Arabia buy 180 M109A5/A6 medium self-propelled howitzers and equipment to convert these into the M109A6 Paladin artillery system.

Separately, the US also approved a $2.5 billion deal to sell NATO ally Germany four MQ-4C Triton maritime surveillance drones.