US President Barack Obama said on Thursday (14 May) that, in the event of a threat to Gulf nations, the United States would consider using military force for their defence.

Obama, speaking after a summit with Gulf leaders at the presidential retreat Camp David, is seeking to reassure them of Washington's iron-clad commitment to their security amid Arab anxiety over US-led efforts to reach a nuclear deal with Iran.

Hosting the six-nation Gulf Cooperation Council for a rare summit at Camp David, Obama pledged that the United States would consider using military force to defend them and would also help address Iran's "destabilising activities in the region."

"The United States is prepared to work jointly with GCC member states to deter and confront an external threat to any GCC state's territorial integrity that is inconsistent with the UN charter. In the event of such aggression or the threat of such aggression, the United States stands ready to work with our GCC partners to urgently determine what actions may be appropriate, using the means at our collective disposal, including the potential use of military force for the defence of our GCC partners," Obama told a closing news conference at the presidential retreat in the Maryland mountains outside Washington.

Obama stopped short of offering a formal defence treaty that some Gulf countries had sought and instead announced more modest measures, including helping them to integrate ballistic missile defensc systems, streamlining weapons sales and increasing military training.

With the United States and five other world powers facing a 30 June deadline for a final deal with Iran on curbing its nuclear program, Obama also sought to allay Gulf Arab fears that the potential lifting of international sanctions on Tehran would embolden it in the region and increase the risk of it fuelling more sectarian strife.

Obama sought to strike a balance between trying to ease Gulf Arab fears about his diplomacy with Shi'ite Iran, their regional arch-rival, and at the same time squeezing the oil-rich states to work together more in their own collective defence.

"There was a concern, a concern that I share that even if we deal effectively with the nuclear issue, that we will still have a problem with some of Iran's destabilizing activities. And a number of them did express the concern that with additional resources through the reduction in sanctions, that was it possible that Iran would siphon off a lot of these resources into more destabilizing activity. Secretary Jack Lew was there to explain that, first of all, there would be no sanctions relief until we could confirm that Iran had actually carried out its obligations under any nuclear deal," Obama said.

The United States also pledged to help the Gulf states beef up "maritime security" in the world's most important oil routes, a clear reference to worries about recent Iranian actions.