Iran will take action against “inhuman” sanctions that make it harder for its passenger planes to refuel abroad and buy spare parts, the Foreign Ministry said on Tuesday.

“Not supplying a passenger plane with fuel is an inhuman action that violates international norms,” ministry spokesman Ramin Mehmanparast told his weekly news conference.

“We have informed the relevant authorities and if a country is acting contrary to the principles, avoiding supplying fuel, we will counter it and take necessary measures.”

National carrier Iran Air started having problems refuelling at European airports last October when many western companies stopped selling it fuel to comply with U.S. sanctions prohibiting the export of refined petroleum products to Iran.

Washington stepped up its sanctions last week, blacklisting Iran Air and a major Iranian port operator, potentially increasing the airline’s problems .

Mehmanparast implied that the U.S. move could make it harder for Iranian carriers to buy spare parts.

An Iran Air Boeing 727 on a domestic flight crashed in January, killing at least 77 people , raising questions about the safety of Iran’s aging civil avation fleet and adding to pressure on Transport Minister Hamid Behbahani who was sacked by parliament in February.

“The embargo imposed on Iran Air, the sale of passenger plane spare parts or the obtaining of facilities such as supplying fuel … is contrary to international norms,” Mehmanparast said.

“The Iranian companies that have sustained losses due to such unilateral actions will definitely follow up the actions … and will seek compensation.”

Iran Air said last October that it would challenge the fuel sanctions in an international court.

The Islamic Republic is subject to four rounds of United Nations sanctions aimed at forcing it to curb its nuclear programme, which many countries believe is aimed at developing the ability to build atomic bombs, a charge Tehran denies.

The United States, the European Union and some other countries have imposed additional sanctions. Tehran rejects the pressure as illegal and ineffective.

Issuing the new sanctions last week, the U.S. Treasury said Iran Air and its Iran Air Tours subsidiary had on numerous occasions transported military-related equipment on behalf of the government, including missiles, rockets and titanium sheets, a dual-use material that can be used in advanced weapons systems.

Tehran denied those accusations as well.

Iran has already retaliated on aviation fuel, denying some European airlines kerosene and forcing them to make additional landings on flights to Europe, as Iran Air has to do. Affected flights include Tehran-London and Tehran-Paris routes.

The Iranian daily Sharq reported on Monday that Iran Air was no longer able to make refuelling stops in Belgrade, a situation that began after Austrian oil and gas group OMV stopped supplying the airline with fuel at Vienna Airport.

The last Belgrade stop was on June 18, Sharq said.