An annual Gulf summit is due to begin Sunday in Riyadh amid a sharp dispute of more than a year between a Saudi-led bloc and Qatar.

The US-allied Gulf Cooperation Council (GCC) comprises Saudi Arabia, the United Arab Emirates (UAE), Bahrain, Kuwait, Oman and Qatar.

In June 2017, Saudi Arabia, the UAE, Bahrain and Egypt severed diplomatic, transportation and economic links with Qatar, accusing it of supporting and funding terrorists, a charge that Doha denied.

The quartet demanded that Doha downgrade ties with Iran, a regional rival of Saudi Arabia. Qatar rejected the demand, calling it an "infringement of its sovereignty."

Attempts by Kuwait and the US to resolve the crisis have failed.

This week, Saudi King Salman bin Abdelaziz invited Qatar's Emir Tamim bin Hamad Al Thani to attend the one-day summit. Turkish state news agency Anadolu reported on Sunday that Tamim would not be attending.

In the run-up to Sunday's meeting, the anti-Qatar alliance has lowered expectations for an imminent end to the row.

"The political crisis will end when its reason ends, namely Qatar's support for extremism and interference in the region’s stability," UAE Minister of State for Foreign Affairs, Anwar Garghash, tweeted on Thursday.

Last year, the GCC summit, originally scheduled for two days in Kuwait, ended hours after it began as Tamim and Kuwaiti Emir Sabah al-Ahmed Al Sabah were the only heads of state attending.

The four other leaders of the group skipped the gathering.

The Qatar row is one of the most serious experienced by the GCC since it was created in 1981.