US President Barack Obama on Friday left Italy for Saudi Arabia - the last stop of his six-day tour of Europe and the Middle East.

The US leader was expected to spend Friday evening in talks with Saudi King Abdullah on a royal estate outside the capital Riyadh, as mistrust fuelled by differences over Iran and Syria overshadows the Saudi-US alliance.

Saudi Arabia has strong reservations about attempts by Washington and other major powers to negotiate a deal with Iran on its nuclear program, and disappointment over Obama's 11th-hour decision last year not to take military action against the Syrian regime over chemical weapons attacks.

Saudi-US relations, dating back seven decades, are "tense due to Washington's stances" on the Middle East, especially Iran, said Saudi analyst Abdel Aziz al-Sagr, who heads the Gulf Research Center.

The recent rapprochement between Tehran and Washington "must not take place at the expense of relations with Riyadh," Sagr told AFP.

Saudi Arabia views the November deal with Iran as a risky venture that could embolden Tehran.

AFP