LONDON — In their long-running rivalry, the United Arab Emirates has often accused its neighbor Qatar of abetting Islamist militants, citing as one prime example the 2013 opening of a Taliban embassy in the Qatari capital, Doha.

Now it turns out that the Emiratis tried to get the Taliban to open an embassy in their own country instead. The Emirati ambassador to Washington, Yousef al-Otaiba, even received “an angry phone call” from the foreign minister at the time complaining that the Taliban had ended up in Qatar and not the U.A.E., according to leaked emails from the ambassador’s account.

The leaks are the latest salvo in a two-month-old feud among the Persian Gulf neighbors that has divided Washington’s allies in the fights against the Islamic State and Iran. In June, the U.A.E., Saudi Arabia, Bahrain and Egypt cut off trade and diplomatic relations with Qatar as punishment for what they said was its support of Islamist extremism. Qatar, the site of the largest American air base in the region, charged that Saudi Arabia and the Emirates were inventing a pretext to bully their neighbor.

Qatar and the U.A.E. have been intense rivals for years, even though they are nominal allies — and both key military partners of Washington. During their recent rift, they have accused each other of meddling in each other’s internal affairs. Supporters of each side have accused the other of cyberespionage. Anonymous hackers have provided a long series of leaked emails from Ambassador Yousef al-Otaiba’s Hotmail account to The New York Times and other news organizations over the past two years in an apparent campaign to embarrass the U.A.E. and benefit Qatar.