The two-day meeting at the Presidential country-retreat of Camp David in the Maryland mountains northwest of Washington, is a rare invitation from Obama to the six members of the Gulf Cooperation Council (GCC).

But the rulers of Saudi Arabia, the United Arab Emirates, Bahrain and Oman are skipping the talks which start on Thursday and instead sending lower-ranking representatives.

On the agenda are the integration of ballistic missile defense architecture, more military exercises to address maritime, counterterrorism, air and missile defense challenges and government infrastructure against cyber hackers, according to US officials.

Saudi Arabia's announcement on Sunday that newly-crowned King Salman would not attend came just two days after White House officials said Obama and the king would hold one-on-one talks in Washington ahead of the Camp David meeting.

Riyadh's explanation has been that the king wants to stay in the Gulf to oversee the five day truce due to begin in Yemen on Tuesday.

Obama and King Salman discussed the summit by phone on Monday, according to the White House. Foreign policy aide Ben Rhodes played down any talk of a rift, saying the two leaders had talked about the "upcoming GCC (Gulf Cooperation Council) summit" at Camp David. They reviewed the summit agenda and agreed on the need to work closely with other Gulf states to address threats facing the region.

Tension denial

Saudi Foreign Minister Adel al-Jubeir joined the White House in denying tensions between the two countries: "This is not related in any way, shape or form to any disagreement between the two countries," Saudi Foreign Minister Adel al-Jubeir said. "I think this idea that this is a snub because the king did not attend is really off base. This is an extremely high level delegation. It has absolutely the right people to represent the Kingdom."

There had been media reports that Saudi Arabia was at odds with the US over its efforts to make a nuclear accord with Iran, a country that Sunni Gulf nations see as a destabilizing actor in the region.

Some of the Gulf nations also want a formal, written agreement with Washington that would require the US to come to their defense if they were to come under attack from Iran or another outside threat. The US has such an arrangement with Japan. But US administration officials have said they can not offer a defense treaty which would meet with opposition in Congress.

jm/bw (Reuters, AP, AFP)