Divisions among Gulf states were exposed when Saudi Arabia’s allies rounded on Qatar for snubbing a personal invite from King Salman and sending a relatively junior foreign minister to the annual Gulf Cooperation Council (GCC) meeting in Riyadh.

Qatar is enduring a 20-month economic, diplomatic and political boycott by Saudi, Egypt, the United Arab Emirates and Bahrain that has soured relations and led to bitter rhetorical war.

Bahrain’s foreign minister openly criticised Qatar’s emir, Tamim bin Hamad Al Thani, in a tweet for his no-show. “Qatar’s emir should have accepted the fair demands [of the boycotting states] and attended the summit,” he said.

The summit, the first since a brief bad-tempered meeting last December, comes at the worst moment of crisis in the 37-year history of the GCC, which was designed as a customs and political union for the six Gulf states.

The quartet of Arab states has accused Qatar of financing terrorism and seeking to undermine Saudi Arabia. Qatar has denied the charges and said the boycott aims to impinge on its independent foreign policy.

At the summit’s opening session, Kuwait, a traditional mediator in the region, urged all sides to end the damaging persistent disunity. Its emir, Sheikh Sabah al-Ahmad al-Sabah, specifically called for an end to the media campaigns he said had planted the seeds of discord in the region.

The level of Qatar’s ministerial delegation was not known until the last minute, with some questioning whether it would attend at all. It was led by the minister of state for foreign affairs, Sultan bin Saad al-Muraikhi.

The emir, Sheikh Tamim bin Hamad al-Thani, was personally invited by King Salman of Saudi Arabia, and his decision not to attend will be seen as significant. The letter from King Salman was the first formal contact between the two countries at such a senior level since the boycott began.

Qatar’s emir, Sheikh Tamim bin Hamad al-Thani, was personally invited to the summit by King Salman. Photograph: Yam G-Jun/AP

Qatar has been critical of Saudi operations in Yemen, supported the Iran nuclear deal signed in 2015 and has expressed its sympathy to the family of Jamal Khashoggi, the murdered Saudi journalist.

In a sign of unabated tensions before the summit, the Bahraini foreign minister accused Qatar of committing itself to Iran, in effect burning its bridges with its GCC partners.

Qatar last week underscored its independence from Saudi Arabia by pulling out of the oil cartel Opec. It is one of Opec’s smallest oil producers but the world’s biggest liquefied natural gas (LNG) exporter and its exit from the oil cartel deepened the sense that a resolution to the Gulf row was unlikely.

The one-day summit is due to discuss strategic military cooperation, including how to approach the Yemen peace talks, including continued support for the joint Saudi-UAE efforts to drive the Houthi-backed militias from power in Yemen.

In the wake of last year’s summit, Saudi and the UAE announced the formation of a joint coordination council that looked as if it might substitute for the GCC, and so formalise Qatar’s isolation.

But at the opening of Sunday’s summit, King Salman said he wanted the GCC, designed as a customs and political union for the six Gulf states, to survive.

A complete boycott of the summit would have risked damaging Qatar’s own standing at a time when Saudi’s traditionally close relations with the US are under pressure over the Saudi court’s involvement in the murder of Khashoggi, a Washington Post columnist.

Commenting ahead of the summit, the Gulf analyst and Chatham House fellow Kristian Ulrichsen said: “The personality-driven policies pushed by the crown princes of Saudi Arabia and Abu Dhabi, Mohammed bin Salman and Mohammed bin Zayed, have fractured Gulf politics in more ways than one.

“Tensions exist also between Kuwait and Saudi Arabia, and between Oman and the UAE, in part over Abu Dhabi’s policies in southern and eastern Yemen and toward the broader Horn of Africa and Indian Ocean littoral.

“Neither Kuwait nor Oman, to say nothing of Qatar, shares the hyper-hawkish approach of Riyadh or Abu Dhabi to regional affairs, and are aware that they may be next to come under pressure to conform to the Saudi-Emirati geopolitical and foreign policy straitjacket.”