I congratulate my former counterpart, Boris Johnson on becoming UK PM," Zarif wrote.
Addressing the issue of Iranian oil tanker detained by the British, the Iranian minister noted that "the May govt's seizure of Iranian oil at behest of US is piracy, pure & simple."
"Iran does not seek confrontation. But we have 1500 miles of Persian Gulf coastline," he added.
"These are our waters & we will protect them," Zarif underlined.
HJ/