Pentagon chief Chuck Hagel holds talks in Bahrain Friday to reassure anxious Gulf allies that the US military will maintain a robust regional presence despite a nuclear deal with Iran.

Defense Secretary Hagel, who flew to Bahrain on Thursday evening, will convey to Gulf leaders at a security conference that the United States remains a steadfast partner and has no plans to scale back its military deployments or weapons sales to the Gulf Arab states, officials said.

"It's a somewhat tense time for the region. There's a lot of questions about US policy, particularly about where things are going in the wake of the Iran interim agreement," a senior US defence official told reporters travelling with Hagel.

In private meetings and in a speech Saturday, Hagel will seek "to reassure our partners here that nothing has changed in our defence posture as a result of the recent negotiation and interim agreement with Iran," said the official, speaking on condition of anonymity.

Hagel will underscore that "we have longstanding commitments here and longstanding partnerships" and "very high ambitions for our defence relations in this part of the world," the official added.

The United States and other world powers reached a November 24 interim agreement with Iran to roll back its nuclear programme in return for limited sanctions relief.

But the accord, coupled with Washington's reluctance to take military action against the Tehran-backed Syrian regime, has raised alarms among mostly Sunni Gulf states that view Shiite Iran as a serious threat.

"There's concern about the Iran interim deal, there's concern about what's happening in Syria," said a second US defence official, who also asked not to be named.

"And this is a perfect opportunity for secretary Hagel... to have a robust and expanded engagement with our Gulf partners to make clear that the US commitment is unwavering, it's unchanged, it's as strong as ever."

Hagel's speech at the annual "Manama Dialogue" organised by the International Institute for Strategic Studies, will offer a chance to make the argument for the interim nuclear deal, while noting that sanctions and a strong US military presence have helped exert pressure on Tehran, officials said.

"We believe we have a very strong case," said the first official. "Its certainly not a mission impossible."

During his flight to Manama, Hagel spoke about Iran with Abu Dhabi Crown Prince Mohammad bin Zayed al-Nahayan, deputy commander of the UAE armed forces, officials said.

Hagel affirmed "the US commitment to the security of the United Arab Emirates and its allies and partners in the Gulf," a Pentagon statement said.

Hagel "underscored the United States commitment to preventing Iran from acquiring a nuclear weapon" and called the interim nuclear accord a "first, good step".

During Hagel's trip, which will also include Qatar, he was due to visit American troops and meet Bahrain's ruling family, Saudi Arabia's deputy defence minister and the foreign ministers of Egypt and the UAE, officials said.

Hagel's tour comes as senior Iranian envoys sought to mend ties in the Gulf, with Foreign Minister Mohammad Javad Zarif visiting Kuwait and unveiling plans to travel to Saudi Arabia.

Hagel is the first US defence chief to visit Bahrain in more than two years, with Washington voicing repeated concerns about the Sunni monarchy's response to protests from the country's Shiite majority.

Bahrain hosts the US Fifth Fleet headquarters, a crucial naval hub that oversees aircraft carriers and other warships patrolling the strategic Gulf sea lanes.

Washington views Bahrain as of "great strategic importance", but has withheld some military assistance as part of an effort to urge Manama "to lift restrictions on civil society" and "engage in a deliberate reform process," US national security adviser Susan Rice said Wednesday.