Saudi Arabia, along with Bahrain and the United Arab Emirates, severed diplomatic ties with Qatar in 2017, accusing it of supporting terrorism and fostering close ties with their regional rival Iran. Doha denies the allegations.
Qatar's emir skipped a summit in Saudi Arabia on Sunday with fellow Arab Gulf leaders whose boycott of the small but energy-flush neighbour has sparked a major regional diplomatic row.
Riyadh is hosting the annual gathering as crises rumble on over the 18-month-old dispute with Doha, the war in Yemen and the murder of journalist Jamal Khashoggi in Saudi Arabia's consulate in Istanbul.
The regional powerhouse had invited Qatari Emir Sheikh Tamim bin Hamad al Thani to attend the six-nation Gulf Cooperation Council talks, but the foreign ministry in Doha said he would not go.
Instead Qatar was represented by the minister of state for foreign affairs, Sultan al Muraikhi, it said.
Saudi Arabia, along with Bahrain and the United Arab Emirates, severed diplomatic ties with Doha in 2017, accusing it of supporting terrorism and fostering close ties with their regional rival Iran.
Doha - which announced this month it was quitting the Saudi-dominated OPEC oil cartel - denies the allegations, but the dispute has dragged on.
Speaking at the summit, Saudi King Salman accused Iran of "continuing to interfere in the affairs of the countries in the region".
He stressed the importance of the GCC and the need to "defend, in collaboration with our partners, security and stability in the Gulf".
The summit's final declaration included a call for "unity", but did not explicitly mention the Qatar crisis.
A Qatari foreign ministry spokesman blasted the communique on Twitter for "not evoking the blockade of Qatar and the means of resolving it".
The GCC was formed in 1981 at the height of the Iraq-Iran war and two years after the Islamic revolution in Tehran sparked concern in Sunni-led Gulf states, many of which have sizable Shia populations, including in Bahrain.
GCC secretary general Abdullatif al Zayani has said the summit would review ties with Iran after the US reimposed an oil embargo and other sanctions on Tehran following Washington's withdrawal from a landmark 2015 nuclear deal.
Saudi prince under pressure
Saudi Arabia, along with allies the UAE and Bahrain, accuses Tehran of fomenting unrest among Shias in the Gulf, and has backed the US in piling pressure on Iran.
This contrasts with Kuwait and Oman which prefer normalising ties with the Islamic republic.
The meeting comes as delegations from Yemen's Saudi-backed government and Iran-linked Shia rebels hold UN-brokered peace talks in Sweden.
Yemen's capital has been held since 2014 by Houthi rebels who drove the government out and seized a string of ports.
The Yemeni government, based in the southern port city of Aden, has fought to push back the rebels with support from a military coalition led by Riyadh and the UAE.
King Salman defended the coalition's intervention in Yemen and called for a "political solution" in the impoverished country.
The conflict has killed nearly 10,000 people since 2015 when the coalition intervened, according to the World Health Organization, though some rights groups say the toll could be five times higher.
The UN calls it the world's worst humanitarian crisis, with as many as 20 million Yemenis facing acute food shortages.
Pressure has been piling up on Riyadh to ease off its offensive, particularly an assault launched in June on the rebel-held port city of Hudaida, a key lifeline for aid entering Yemen.
The summit comes with Saudi Arabia and its de facto ruler, Crown Prince Mohammed bin Salman, under mounting pressure over the murder of Washington Post columnist Jamal Khashoggi.
A critic of the crown prince, Khashoggi was killed by a hit squad in the Saudi consulate in Istanbul on October 2 in what the kingdom described as a rogue operation.
Riyadh has steadfastly denied claims the grisly murder of the Saudi journalist was ordered by Prince Mohammed.