Secretary of State John Kerry is seeking to repair frayed ties with Saudi Arabia over the Syrian conflict and Iran, after making his first visit to Egypt since the army ousted president Mohamed Morsi.

The top US diplomat landed in Riyadh late Sunday on the second stop of an 11-day trip which has become an exercise in damage control, as the regional turbulence unleashed by the Arab Spring stirs tensions with longtime US partners.

Saudi Arabia, locked in a decades-long rivalry with Iran, is concerned that proposed Syrian peace talks could leave a Tehran-backed regime in Damascus and that a breakthrough in nuclear negotiations could lead to a US rapprochement with Iran.

The conservative oil-rich kingdom has grown increasingly nervous over the past two years as popular revolts have toppled onetime allies in Egypt, Tunisia and Yemen and spread turmoil across the region.

In an unprecedented move last month, Saudi turned down a coveted non-permanent seat on the UN Security Council in protest at the world body's failure to end the war in Syria, which has left over 120,000 people dead.

Earlier Sunday in Cairo, Kerry acknowledged that while there might be differences over "tactics" in ending the Syrian conflict, the goal for the United States and its allies was the same -- a transition of power.

US backs Egypt's interim rulers

Kerry was in the Egyptian capital to meet with the country's interim rulers and urge them to press ahead with reforms and restore democracy.

"We are committed to work with and we will continue our cooperation with the interim government," Kerry told a joint news conference with Egyptian Foreign Minister Nabil Fahmy, stressing that ensuring stability was the key to revitalising Egypt's economic growth.

While he did not raise the case against Morsi whose trial opens Monday, Kerry repeatedly called for inclusiveness, US officials said, and warned that politically motivated trials "are not acceptable" to the United States.

Kerry -- who in a rare move among allies slipped into Egypt unannounced and stayed for only about six hours -- also played down Washington's suspension last month of part of $1.5 billion in annual US aid to Cairo.

He denied the decision had been taken to punish Egypt's military leaders and said it "is a very small issue between us."

Saudi Arabia, one of the main backers of the Syrian opposition, was reportedly angered when US President Barack Obama last month put on hold threatened military strikes against Syrian President Bashar al-Assad's regime.

Kerry also said the US would stick with its friends as they navigate the turmoil unleashed by the Arab Spring, which has led to the rise of powerful new extremist groups in Libya and Syria.

"We will be there for Saudi Arabia, for the Emirates, for Qataris, for the Jordanians, for the Egyptians and others. We will not allow those countries to be attacked from outside. We will stand with them," he told reporters.

'They're very clear about their concerns'

Kerry was to be greeted Sunday by Saudi Foreign Minister Saud al-Faisal and have his first meeting since becoming secretary of state in February with Saudi King Abdullah on Monday.

Washington has been discussing with Riyadh the "best way to ensure support for the Syrian opposition coalition, and the military wing of the Syrian coalition," a State Department official said.

Kerry, working with his Russian counterpart Sergei Lavrov and UN special envoy Lakhdar Brahimi, has been trying to convene peace talks in Geneva aimed at bringing in a transitional government in Syria.

Major groups in the Syrian opposition have so far refused to sit down with members of the Assad regime, insisting his resignation must be on the table, a demand rejected by Damascus.

Saudi Arabia has also eyed warily international moves to engage arch-foe Iran on its nuclear programme following the election of President Hassan Rouhani, a reputed moderate who held a landmark phone call with Obama in September.

"They're very clear about their concerns. We frankly completely agree with the Saudis about their concerns," the State Department official said.

Analysts said that while ties between the two allies are strained at the moment they are unlikely to break completely.

"Despite the Saudi outcry, the bedrock of US and Saudi ties -- intelligence coordination and military containment of Iran -- is solid," Frederic Wehrey, senior associate in the Middle East program at the Carnegie Endowment for International Peace wrote.