WASHINGTON — The United States on Friday sanctioned more than 25 businesses, banks and individuals suspected of working to expand Iran’s nuclear program, supporting terrorism and helping Iran evade US and international sanctions.

The action is part of the Obama administration’s effort to show it will enforce existing sanctions even as it works with other world powers to negotiate a deal that will curtail Iran’s nuclear program.

“Treasury’s action against over 25 entities and individuals, who are involved in expanding Iran’s proliferation program, supporting terrorism in the region and helping Iran evade US and international sanctions, reflects our continuing determination to take action against anyone, anywhere, who violates our sanctions,” Under Secretary for Terrorism and Financial Intelligence David Cohen said in a statement.

As a result of the action, Americans are banned from engaging in transactions with any of the designated parties and blocks all their property or interests in property under US jurisdiction.

Also Friday, the chief of Iran’s Revolutionary Guard navy confirmed in remarks that a US Coast Guard vessel fired on an Iranian fishing boat in the Persian Gulf this week but insisted the incident was not a “clash.”

The US Navy’s Bahrain-based 5th Fleet said that personnel on a small boat dispatched from the US Coast Guard patrol boat Monomoy fired a single shot on Tuesday when they saw the crew on a nearby Iranian dhow training a .50-caliber machine gun on them and preparing to fire.

No one was hurt in the encounter, which came as the two countries work to hammer out a lasting deal over Iran’s nuclear program.

The shot from the US patrol boat was fired “in the air about three miles away” from the Iranian boat, Adm. Ali Fadavi of Iran’s Guard was quoted as saying by the Tasnim News Agency.

“It wasn’t a clash but a single shot in the air … there was no clash between Iranian and American forces,” Fadavi said, adding that “Americans feared and felt danger from a fishing dhow.”

Dhows are traditional wooden boats common to the region that are typically used for trade and fishing.

American, Iranian and other countries’ military vessels routinely patrol the Persian Gulf, a key route for international oil shipments, usually without incident.

Speed boats from Iran’s Guard, however, have passed close to US ships in incidents that have raised alarm in Washington.

Fadavi, the Iranian officer, also said the Americans “should be fearful” as long as they are present in the Gulf. Tehran has long decried the US presence in the critical waterway as a source of tension in the region.

The West and Israel believe Iran’s nuclear program is aimed at building an atomic weapon. Iran denies the charge, saying its nuclear activities are for peaceful purposes only, such as power generation and medical research.