Gulf Arab leaders gather in Saudi Arabia on Tuesday for a summit that is expected to see formal agreement towards ending a long-running dispute with Qatar that shattered Gulf unity at a time of heightened regional tensions with Iran.

Riyadh, the United Arab Emirates, Bahrain and non-Gulf Egypt severed diplomatic, trade and travel ties with Qatar in mid-2017 over allegations Doha supports terrorism. Qatar denies that and says the boycott aims to curb its sovereignty.

Qatar's Emir Sheikh Tamim bin Hamad al-Thani headed to al-Ula, where the summit is being held, state media reported, after an announcement that Saudi Arabia would reopen its airspace and sea and land border to Qatar under a deal that a senior US official said would be signed on Tuesday.

Bahrain will be represented by its crown prince instead of the king at the annual summit and the UAE delegation is headed by the federation's vice-president, who is also ruler of Dubai.

While Saudi Arabia made clear it intended to lift the embargo, the other three countries did not immediate comment in on the issue, but the US official said "it's our expectation" they would also join. Under the emerging deal, Qatar will suspend lawsuits related to the boycott, the official said.

All of the countries are US allies. Qatar hosts the region’s largest US military base, Bahrain is home to the US Navy’s Fifth Fleet, and Saudi Arabia and the UAE host US troops.

The development is the latest in a series of Middle East deals sought by Washington - the others involving Israel and Arab states - aimed at building a united front against Iran.

White House senior adviser Jared Kushner, assigned to work on the dispute by President Donald Trump, is due to attend the ceremony in the historical city of al-Ula along with Middle East envoy Avi Berkowitz and Brian Hook, a special State Department adviser