The UN's top court on Thursday rejected a case brought by Qatar accusing the United Arab Emirates of discrimination during a blockade of Doha, which has since been lifted.

Qatar filed the case in 2018, a year after Saudi Arabia, the UAE, Bahrain and Egypt cut land, air and sea links over claims the gas-rich nation backed Islamists and was too close to Iran.

Qatar's rivals agreed to lift the restrictions at a summit in January and the UAE reopened its borders to Qatar days later, while adding it would take longer to fully rebuild trust.

Doha had said the UAE's actions during the three-year blockade had breached the 1965 International Convention on the Elimination of All Forms of Racial Discrimination (CERD), a UN treaty.

But the International Court of Justice said that it "upholds the first preliminary objection raised by the UAE" that racial discrimination did not include nationality under the terms of the convention.

"The court finds that it has no jurisdiction to entertain the application filed by the state of Qatar," ICJ President Abdulqawi Ahmed Yusuf said in The Hague.

He said the UAE's measures "are not capable of constituting racial discrimination within the meaning of the convention."

The quartet agreed to lift the restrictions on January 5 at a summit in the Saudi desert after a flurry of diplomatic activity by then-US President Donald Trump's administration.

The United Arab Emirates, the staunchest critic of Qatar and its leadership throughout the crisis, was seen as a reluctant party to the rapprochement.

But it became the first to reopen its borders to Qatar, followed days later by Saudi Arabia and Egypt

Qatar and the UAE traded bitter accusations during the case at the ICJ, which was set up after World War II to rule in disputes between member states.

The UAE accused Qatar of backing "terrorism and extremism". Doha then alleged its rival was "inflicting maximum suffering on the Qatari people."

The case had previously gone Qatar's way, with the ICJ in 2018 ordering the UAE to take emergency measures to protect the rights of Qatari citizens while it dealt with the wider lawsuit.

The court also rejected a bid by the UAE to seek its own emergency measures to stop Qatar "aggravating" the case.

Doha further won a separate but related case at the ICJ in July that was specifically about the air blockade, based on international air travel rules.