TEHRAN, Iran—Iran says it is installing new and efficient centrifuges aimed at speeding up its nuclear enrichment, the spokesman for the Iranian Foreign Ministry, Ramin Mehmanparast, announced on Tuesday.

The move comes despite four rounds of United Nations Security Council sanctions over Tehran’s refusal to halt enrichment.

Iran says it wants to enrich only to power a future network of reactors and medical isotopes. Over the past two years it has started to enrich uranium to a level closer to the grade used to make the fissile core of nuclear warheads.

The West suspects Iran is pursuing a nuclear weapon program, a charge that Iran denies.

Meanwhile, a prominent Iranian hard-liner has called for attacks against US and European airline offices over their refusal to supply fuel to Iranian aircraft.

Hossein Shariatmadari, a representative of Iran’s Supreme Leader Ayatollah Ali Khamenei, says in an editorial in his Kayhan daily on Tuesday that American and European airlines should be “taught an unforgettable lesson.”

Iran already has banned the supply of jet fuel to European airlines in a tit-for-tat move.

Iran is at odds with the West over its nuclear program. Tehran’s refusal to halt uranium enrichment has brought four sets of UN sanctions against Iran.

The US and its allies accuse Iran of seeking to build nuclear weapons, a charge Tehran denies.