TEHRAN, Iran -- Iran's supreme leader on Thursday slammed the new U.S. sanctions on Tehran signed by President Donald Trump the previous day, and vowed his country would continue its missile program despite international pressure.

Washington will "use any excuse to make a fuss" against Iran, said Ayatollah Ali Khamenei, speaking at a ceremony marking the formal endorsement of President Hassan Rouhani for his second term in office.

"You launch a satellite-carrying missile, they make noise," he said, describing the Iranian launch as a "scientific and technical job that is routine and necessary."

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"The response to the hostility is to become stronger," Khamenei added and described the U.S. government as "the top aggressor and the most shameless "enemy of Iran.

"Some have sharply applied hostility (against Iran), like those who today are in office in the U.S.," Khamenei said, without mentioning Trump or the U.S. president's signing of the legislation on Wednesday.

The law also imposed new sanctions on Russia and North Korea.

According to a letter sent to the U.N. Security Council and obtained Wednesday by The Associated Press, the United States and three Western allies called Iran's recent launch of a satellite-carrying rocket "a threatening and provocative step" that is "inconsistent" with a U.N. resolution endorsing the 2015 nuclear deal with world powers.

Iran last week launched the country's most advanced satellite-carrying rocket into space, marking the most significant step forward for the Islamic State's young space program.

In the letter to the Security Council, the U.S., France, Germany and the United Kingdom complained that the Simorgh space launch vehicle, if configured as a ballistic missile, would have the range and "payload capacity to carry a nuclear warhead."

Iran maintains the 2015 nuclear deal that put caps on its uranium enrichment program - a possible pathway to nuclear weapons - and the Security Council resolution endorsing that deal do not ban the country from ballistic missile activity. Russia, one of the five world powers that brokered the nuclear deal, has agreed with Tehran.

On Tuesday, Iran's Parliament Speaker Ali Larijani announced that Tehran has officially complained to the U.N. Security Council over the latest U.S. sanctions.

Khamenei, who has final say on all state matters, said Iran should continue to stand powerful in the face of its enemies.

"International engagement should not lead to ignoring hostility of the enemies," Khamenei said at the ceremony, broadcast live on state TV. He added that "despite all the sanctions and enmities, the Islamic Republic is stronger" than before.

Rouhani, who will be formally sworn into office on Saturday in parliament, said the nuclear deal has been a sign of "good faith" by Iran and that t brought the nation respite from most difficult U.N. sanctions.

"Transition from the most difficult sanctions was achieved through a combination of the power of diplomacy and deterrent defensive power," said Rouhani. He said that in his second term in office, Iran will "insist on constructive engagement with the world more than before."

Earlier Thursday, the state TV website quoted deputy foreign minister and senior nuclear negotiator Abbas Araghchi as saying that Iran will come up with a "smart" reaction to the last U.S. sanctions.

Araghchi reiterated Iran's stance that the U.S. legislation signed by Trump amounts to a "hostile" breach of the landmark 2015 nuclear deal. Tehran has prepared measures that Iran would take against the U.S. action, he added without elaborating, except to say some of the measures will "improve" Iran's armed forces.

The U.S. legislation imposes mandatory penalties on people involved in Iran's ballistic missile program and anyone who does business with them. It would also apply terrorism sanctions to Iran's prestigious Revolutionary Guard and enforce an arms embargo.