US Secretary of State John Kerry will help ink a major estimated $2.1 billion proposed deal with Oman to supply a US-made air-defense system to the Gulf nation, officials said Tuesday.

One of the main focuses of Kerry's trip to Muscat was to applaud the signing of a letter of intent between Oman and US manufacturer Raytheon ahead of talks on the final contract, they told reporters traveling with him to Oman.

"In January the Omanis made a decision to buy a ground-based air defense system produced by Raytheon ... something that the secretary advocated for when he was in the Senate," a senior State Department official said.

Kerry had strongly backed the bid by the company based in his home state of Massachusetts, before taking office as the new top US diplomat on February 1.

"Part of the goal of this is to push US commercial interests, to demonstrate to Oman that these are important to this administration," the official added.

The letter of intent is expected to be signed Wednesday, with Kerry due to hold talks later Tuesday with Oman's Sultan Qaboos.

The final details of the deal have yet to be worked out, but officials said the contract would be worth an estimated $2.1 billion.

"It will further integrate the defensive systems in the Gulf, which is something we have been working on quite a bit within the GCC," the official said, referring to the Gulf Cooperation Council.

"There are similar systems elsewhere in the Gulf," she said.

"Oman has also recently brought a second tranche of F-16s so this is a way of continuing our relationship in the defense arena and will have pluses in terms of interoperability."

US officials said the deal to supply 12 F-16s was sealed in 2011 for delivery through 2014.

Kerry will also discuss the war in Syria with its key Gulf ally, which maintains close ties to Iran.

The US and the West has condemned Iran for helping to prop up Syrian President Bashar al-Assad in his bloody fight to stay in power against a determined rebellion now in its third year.

The United States and Russia are working to bring together the Assad regime and the opposition at the conference to map out a path for a political transition and end the war which has claimed over 94,000 lives.

Russia has insisted Iran should be invited to the peace conference, although a date and venue has not yet been agreed. But the West is wary of engaging Tehran in such global efforts.

"Oman is not a key player in Syria, but as an important player in the Gulf it will be good to hear the sultan's views on the situation in the region writ large," the State Department official said.

"So it's a chance basically to do a signals check with an important ally."

But she cautioned against the notion that Washington could be seeking to tap into Muscat's influence with Iranian leaders.

"It's true that Oman does maintain a rather unique relationship with Iran, which is not all that surprising given geography," the official said. But "this is not meant to be a trip to focus on Iran," she added.

Kerry will then head to Amman for a meeting of the Friends of Syria group on Wednesday.

While the beginning of his eight-day trip is likely to focus on Syria, Kerry then travels for talks Thursday and Friday in Israel and with the Palestinian leadership.

He is seeking to kickstart the peace process, which has languished for more than two years, with a series of parallel moves aimed at restoring trust.

There remains deep skepticism over whether Kerry can break the deadlock and bring the two sides back to negotiations -- let alone whether he can then help broker a peace deal.

But he has brought a renewed emphasis to the dossier, and will have traveled the same number of times to Israel as Clinton did in her whole four-year tenure.

In a further measure of the renewed US commitment to the Middle East, after a brief stop at the weekend in Ethiopia for celebrations to mark the 50th anniversary of the African Union, Kerry will return to Jordan.

He is to attend a World Economic Forum meeting at which he may outline his plans to revive the crippled Palestinian economy.