Iran will react with equal countermeasures if Washington tries to block its oil exports, the foreign ministry said on Tuesday, while the Islamic Republic’s armed forces chief said U.S. threats would draw an “unimaginable and regrettable” reaction.

U.S. officials are stepping up diplomatic efforts to pressure countries to stop importing Iranian oil.

“If America wants to take a serious step in this direction it will definitely be met with a reaction and equal countermeasures from Iran,” foreign ministry spokesman Bahram Qassemi was quoted as saying by the state news agency IRNA.

Supreme Leader Ayatollah Ali Khamenei on Saturday backed President Hassan Rouhani’s suggestion that Iran might block Gulf oil exports if its own exports are stopped.

Already fraught relations between Tehran and Washington have worsened in recent days.

Armed Forces Chief of Staff Major General Mohammad Bagheri said on Tuesday that Iran wants peace but will defend its interests in the Gulf.

“As the dominant power in the Persian Gulf and the Strait of Hormuz, (Iran) has been the guarantor of the security of shipping and the global economy in this vital waterway and has the strength to take action against any scheme in this region,” Bagheri said.

On Monday, Iran dismissed an angry warning from President Donald Trump that it risked dire consequences “the like of which few throughout history have suffered before” if it made threats against the United States.

Bagheri said that U.S. threats against Iran will draw a “strong, unimaginable and regrettable” response from Tehran, according to the IRNA news agency.

“As our president correctly pointed out, the enemies, particularly America, whose centers of interest are within reach of the visible and hidden defense forces of the Islamic Republic of Iran, should not play with the lion’s tail,” Bagheri said in a statement, according to IRNA.

“Because they will receive a strong, unimaginable and regrettable response of great magnitude in the region and the world.”

Separately, Iran’s parliamentary speaker on Tuesday described Trump’s comments as “the words of a troublemaker”.

“The United States is experiencing disorder and wildness in its diplomatic relations,” Ali Larijani was quoted as saying by IRNA.

Iran has faced the threat of U.S. sanctions since Trump decided in May to withdraw the United States from a 2015 agreement between world powers and Iran over its disputed nuclear program.