The US Treasury Department warned foreign financial institutions Monday that continuing to conduct business with Iran or its financial sector could expose them to American sanctions without prior warning.

"Foreign financial institutions continuing to transact with sanctioned Iranian financial institutions could be targeted at any time without advance notification and should take immediate action to terminate such activity and relationships," the Treasury Department said in an alert quoted by Reuters.

Iran was already subject to extensive US sanctions before the war began in February. In recent weeks, however, Washington has stepped up pressure on foreign governments and businesses to sever economic ties with Tehran or risk losing access to the US dollar-based financial system.

According to the Treasury notice, foreign financial institutions that help Iran access international financial markets, including by providing services to Iranian banks, their subsidiaries or branches in third countries, could be sanctioned for supporting sanctioned sectors of the Iranian economy. They could also face civil or criminal enforcement action if Iran-related transactions cause US financial institutions or other American persons to violate sanctions.

Among the measures Washington could impose are "strict conditions" prohibiting foreign financial institutions from opening or maintaining US correspondent or payable-through accounts if they engage in sanctioned activities.

The warning comes as Treasury Secretary Scott Bessent pursues “Operation Economic Outcast," a campaign announced in August designed to economically isolate Iran. The effort is being conducted alongside a US Navy blockade that President Donald Trump reimposed in July.

Bessent has said Washington will continue increasing economic pressure on Tehran until the Iranian government agrees to a peace deal with President Trump. He has also warned that the United States will target assets linked to Iran's Islamic Revolutionary Guard Corps (IRGC).

“We are going to economically asphyxiate this regime," Bessent said in September, adding, “My job is to make sure that they want to have a deal, and they will want to have one."

Bessent said the Treasury Department had located IRGC-linked assets around the world and signaled that they could become targets of US action.

“We are tracking down the IRGC’s assets, and I will say it on worldwide TV, just so you know: We know where in the British Virgin Islands your accounts are at these trust companies," he stated.