Pakistan Prime Minister Shehbaz Sharif on Wednesday appointed Bilawal Bhutto-Zardari, son of assassinated former premier Benazir Bhutto, as foreign minister, giving his coalition ally a senior role in repairing frayed ties with the United States and other Western countries.

Bhutto-Zardari, 33, chief of the Pakistan Peoples Party (PPP), will accompany Sharif on Thursday on a visit to Saudi Arabia to boost trade and investment, in an effort to mend a yawning current account deficit and falling foreign reserves.

President Arif Alvi took the oath from the Oxford-educated Bhutto-Zardari, widely considered a forward-looking, liberal politician and the scion of the country's leading political dynasty.

His mother Benazir was assassinated at an election campaign rally in 2007, and his grandfather Zulfikar Ali Bhutto -- also a former foreign minister and later prime minister -- was hanged by a military dictator in 1979.

Benazir's killer has never been caught, and a U.N. inquiry found that Pakistani authorities had failed to protect her or properly investigate her death.

Sharif announced a 41 member Cabinet after he took over from ousted premier Imran Khan earlier this month. Khan has alleged that the United States backed a conspiracy to topple him just because he refused Washington's advice not to visit Russia in February, a charge Washington denies.

Pakistan's foreign office and its military and civil leadership also rejected Khan's allegations.

The trip to long-time ally Riyadh starting on Thursday is Sharif's first international visit as prime minister.

A statement from Sharif's office said he would have talks with Saudi leaders "with particular focus on advancing economic, trade and investment ties and creation of greater opportunities for the Pakistani workforce in Saudi Arabia."

The two sides will also discuss a range of regional and international issues of mutual interest.

Sharif is likely to seek financial support from Riyadh to help build the country's foreign reserves, which have fallen to $10.8 billion, hardly enough to pay for two months of imports.

Sharif's newly appointed Finance Minister, Miftah Ismail, has said Pakistan faces widening fiscal and current account deficits, falling foreign exchange reserves and high inflation.

(Reporting by Asif Shahzad, Editing by William Maclean)