Saudi Arabia will reopen its borders and airspace to Qatar, US and Kuwaiti officials said Monday, a major step towards ending a diplomatic rift that has seen Riyadh lead an alliance isolating Doha.

The bombshell announcement came on the eve of the six-nation Gulf Cooperation Council (GCC) annual summit in the northwestern Saudi Arabian city of Al-Ula, where the dispute was already set to top the agenda.

Nayef al-Hajraf, secretary-general of the Gulf Cooperation Council (GCC), addresses the Manama Dialogue security conference in Bahrain's capital on December 6, 2020. (Photo: AFP)

In another sign the three and a half year spat was nearing resolution, the office of Qatari Emir Sheikh Tamim bin Hamad Al-Thani said that he would attend, after he skipped the annual meetings for the last three years.

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

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

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

Kuwaiti Foreign Minister Ahmad Nasser Al-Sabah announced on state TV 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."

He noted that the agreement was based on a proposal by Kuwaiti emir Sheikh Nawaf al-Ahmad Al-Sabah, reflecting the nation's repeated efforts to mediate in the crisis.

Drivers in south Doha on the usually calm Salwa highway towards the Saudi border at Abu Samra sounded their horns and waved their arms from their car windows in the wake of the announcement, an AFP correspondent saw.

Regional analyst Michael Stephens, however, said there was still work to be done to bridge the wider divisions between Qatar and its regional rivals and doubted that anything formal had been agreed.

"It's positive news, though. A big step, and the important first step," he told AFP.

The GCC is a bloc that consists of boycotting countries Saudi Arabia, the United Arab Emirates and Bahrain, neutral Kuwait and Oman, and Qatar.