WASHINGTON (Reuters) - The United States on Friday imposed sanctions on 14 people and 17 entities connected to an Iranian research organization it said had played a central role in the country’s past nuclear weapons effort and which remains active.

Among those designated for sanctions was the Shahid Karimi group, which works on missile and explosive-related projects for Iran’s Organization of Defensive Innovation and Research, and four associated individuals, the U.S. Treasury Department said in a Statement.

The United States charges that the organization, known by its Farsi acronym SPND, oversees nuclear-relevant research for Iran and is active in the training of new scientists. It sanctioned SPND’s head, Mohsen Fakhrizadeh, in 2008.

The announcement coincided with a visit on Friday by U.S. Secretary of State Mike Pompeo to Beirut, where he will focus on Lebanon’s ties to the heavily armed, Iran-backed Hezbollah.

“The U.S. government is taking decisive action against actors at all levels in connection with Iran’s Organization of Defensive Innovation and Research (SPND) who have supported the Iranian regime’s defense sector,” Treasury Secretary Steven Mnuchin said.

An administration official, who spoke on a conference call on condition of anonymity, warned that any association with SPND or its subordinate groups “makes them radioactive” and open to U.S. sanctions.

A second official said the sanctions were aimed at trying to pressure Tehran to negotiate a more comprehensive nuclear deal with the United States.

“It is not just putting pressure on Iran to reach a diplomatic negotiated solution, we are highlighting continued existence of the SPND,” the official said.

In his first year in office in 2017, President Donald Trump withdrew the United States from the Joint Comprehensive Plan of Action (JCPOA) signed in 2015 between Iran and six world powers, which aimed to curb Iran’s nuclear program.

France, Britain, Germany, China and Russia remain part of the nuclear agreement, despite the reimposition of sanctions by the United States against Iran.

The crux of the deal, negotiated over almost two years by the Obama administration, was that Iran would restrain its nuclear program in return for the relaxation of sanctions that had crippled its economy. Trump considered it flawed because it did not include curbs on ballistic missiles or regional activity.

Friday’s steps target current SPND subordinate groups, supporters, front companies, and associated officials. The move freezes any U.S. assets of those targeted and bans U.S. dealings with them.

“Today’s action serves as a warning to individuals and entities considering dealing with the Iranian regime’s defense sector in general, and SPND in particular: by engaging in sanctionable activity with designated Iranian persons, you risk professional, personal, and financial isolation,” the U.S. Treasury said in a statement.

Iran’s Supreme Leader Ayatollah Ali Khamenei said on Thursday that Tehran was determined to boost its defense capabilities despite mounting pressure from the United States and its allies to curb its ballistic missile program.