Abu Dhabi and Doha had been locked for years in a bitter rivalry over regional influence.
Qatar and the United Arab Emirates' respective embassies reopened on Monday to resume work after the two Gulf states agreed to restore diplomatic ties, Qatar's foreign ministry said.
The restoration of ties comes amid a broader regional push for reconciliation and more than two years after Arab states ended a boycott of Doha that had shattered the Western-allied Gulf Arab bloc.
The Qatari ministry said in a statement that the two foreign ministers, Sheikh Mohammed bin Abdulrahman Al-Thani and Sheikh Abdullah bin Zayed, had held a phone call as the two embassies reopened on Monday.
Reuters reported in April that the two Gulf states were in the process of restoring diplomatic relations.
Abu Dhabi and Doha had been locked for years in a bitter rivalry over regional influence, the role of Islam in politics and over support for pro-democracy movements across the Middle East.
In 2017, Saudi Arabia, the UAE, Bahrain and Egypt severed all ties with Qatar over accusations that it supported terrorism, a reference to political Islam, and that it had forged closer ties with Iran. Doha denied the charges.
Riyadh and Cairo were the first to reappoint ambassadors to Doha in 2021 after a Saudi-led deal to end the feud, while Bahrain has yet to reopen its embassy in Doha.
The restoration of ties also came after Iran and Saudi Arabia agreed to re-establish relations after years of hostility, which had threatened instability in the Gulf and stoked the war in Yemen.
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