Instead of the Saudi monarch, the kingdom's delegation at the large summit set for Thursday will be led by crown prince and interior minister Mohammed bin Nayef.

The switch is "due to the timing of the summit, the scheduled humanitarian ceasefire in Yemen and the opening of the King Salman Center for Humanitarian Aid," Saudi Arabia's embassy in Washington said Sunday.

The king's son, deputy Crown Prince Mohammed bin Salman, will also be present at the meeting.

Welcome guests

The statement comes only two days after the White House said King Salman would personally attend the gathering and talk to Obama in a one-on-one meeting beforehand.

However, a senior US official said the monarch's decision to skip the gathering was "not in response to any substantive issue," indicating that the Obama administration did not regard it as a diplomatic slight.

"We first learned of the king's possible change of plans from the Saudis on Friday night," the official said, adding that the authorities "look forward to welcoming Crown Prince Mohammed bin Nayef and Deputy Crown Prince Mohammed bin Salman."

Defense against Iran

The planned summit at presidential retreat at Camp David is set to include leaders from Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates.

The meeting is aimed to shore up trust between Washington and its Arab allies, who grow anxious over Iran nuclear deal and Tehran's allegedly rising influence in the region.

Last week, a US source said that Obama was expected to make a new push towards helping the Gulf countries to create a region-wide defense system against Iranian missiles.

'Gentleman's agreement'

This offer could be accompanied by enhanced security commitments, more weapons sales and more joint military exercises, according to US officials, as Obama tries to reassure the Arab partners that Washington is not abandoning them.

"I think we are looking for some form of security guarantee, given the behavior of Iran in the region, given the rise of the extremist threat," said Yousef al-Otaiba, the United Arab Emirates' ambassador to the United States.

"In the past, we have survived with a gentleman's agreement with the United States about security. I think today, we need something in writing. We need something institutionalized," he said.

At the same time, full security treaty with Saudi Arabia or its neighbors remains unlikely, as it could further strain the relationship with Israel, America's main ally in the Middle East.

dj/bw (Reuters, AFP, dpa, AP)