LONDON — Qatar restored full diplomatic relations with Iran on Thursday, the latest volley in an 11-week-old geopolitical feud that has set the tiny yet fabulously wealthy Persian Gulf nation against its neighbors and rattled a previously placid part of the Middle East.

Qatar’s Foreign Ministry announced that it was sending its ambassador back to Tehran after a 20-month hiatus that started in January 2016, when Qatar broke off relations after attacks on two Saudi diplomatic facilities in Iran.

The Qataris gave no explanation for the sudden move. But the timing suggested a purposeful snub of Saudi Arabia, which along with three other countries began a punitive boycott of Qatar in June, accusing it of supporting terrorism and having a too-cozy relationship with Iran. Saudi Arabia, the United Arab Emirates, Bahrain and Egypt cut their air and sea routes to Qatar, and closed its only land border, with Saudi Arabia.

Mediation by the United States, Kuwait and Germany has failed to resolve the feud in the gulf, the one corner of the Middle East that has been largely free of war, refugees or political turmoil in recent years. Analysts said the partial blockade has badly weakened the six-nation Gulf Cooperation Council and threatens to undermine regional stability.