Iran is committed to its obligations under an international nuclear deal despite the US withdrawal from the landmark agreement, its foreign minister said on Thursday, calling the reimposition of sanctions by Washington “unacceptable”.

Foreign Minister Mohammad Javad Zarif made the comments in a meeting with his Japanese counterpart in Tokyo as tensions rise in the Middle East, fuelling concerns that the United States and Iran are heading for conflict.

He was referring to the Joint Comprehensive Plan of Action signed in 2015 by the United States, Iran and other countries, under which Tehran curbed its uranium enrichment capacity and won sanctions relief in return.

President Donald Trump withdrew the United States from the nuclear deal last year and is ratcheting up sanctions on Iran, aiming to strangle its economy by ending its international sales of crude oil. Japan was a major buyer of Iranian oil for decades before the sanctions.

An attack on four oil tankers in the Gulf on Sunday, for which no one has claimed responsibility, and Saudi Arabia’s announcement on Tuesday that armed drones hit two of its oil pumping stations have raised tensions.