Saudi King Salman bin Abdulaziz Al Saud delivers his closing remarks at the G20 summit in Riyadh, Saudi Arabia, on Nov. 22, 2020. The Group of 20 (G20) Saudi Arabia's Presidency said on Sunday the G20 Riyadh Summit reaffirmed the spirit of cooperation, which has always been the cornerstone of the G20 successes. (G20 Saudi Arabia/Handout via Xinhua)

Gulf leaders flew to Saudi Arabia Tuesday for a summit that could yield more breakthroughs in a regional crisis, after Riyadh re-opened its borders to Doha despite lingering enmity between the neighbors.

Saudi Arabia led a coalition of countries in the Gulf and beyond that cut ties and transport links with Qatar in June 2017, charging that it was too close to Iran and backed radical Islamist groups - allegations Doha has always denied.

Those countries, along with Oman and Kuwait which have mediated between the two sides, will meet in the Saudi city of Al-Ula, after the concessions raised hopes for a wider deal.

"Confidence building measures seem to start with Saudi and Qatar, but the rest will join even if later," said Kuwait University assistant professor Bader al-Saif. "Any step toward reconciliation is better than no step at all. The Gulf Cooperation Council (GCC) requires a major reset and can offer much more than it has."

Washington has intensified pressure for a resolution to what Doha calls a "blockade," insisting Gulf unity is necessary to isolate US foe Iran as the curtain falls on Donald Trump's presidency.

Jared Kushner, Trump's son-in-law and senior adviser who shuttled around the region to seek a deal, will attend the signing on Tuesday of the "breakthrough" agreement, a US official said.

"The Trump administration will claim this as another victory for sure," said Royal United Services Institute analyst Tobias Borck, stressing that the two sides have not yet normalized relations.

Kuwaiti Foreign Minister Ahmad Nasser Al-Sabah announced on state television late Monday that "it was agreed to open the airspace and land and sea borders between the Kingdom of Saudi Arabia and the State of Qatar, starting from this evening."

The Saudi-led GCC hawks, along with Egypt, in 2017 closed their airspace to Qatari planes, sealed their borders and ports, and expelled Qatari citizens.

An information battle raged online with the two camps trading allegations and barbs, deepening the resentments.

Observers have warned that the UAE could be the spoiler for reconciliation attempts, having heaped criticism on Qatar and its leadership.