CNN  — 

The FBI helped Moldovan authorities three times in the last five years to thwart potential smuggling of nuclear and radioactive material, a Moldovan interior minister said Wednesday.

The cases in the former Soviet republic involved sting operations, and no one from jihadi groups was involved, a U.S. law enforcement official familiar with the investigations said.

But officials were concerned that smugglers would try to sell to extremist groups such as ISIS, the U.S. source said, and the cases offer a glimpse at efforts to keep such materials – which in some cases could be used for weapons – from being sold on the black market.

U.S. Rep. Adam Schiff, a California Democrat and ranking member on the House Intelligence Committee, said officials have been long concerned about radioactive and nuclear material being smuggled out of the former Soviet Union.

“We know that these radical Islamic groups like al Qaeda and ISIS would love to get their hands on radioactive materials to fashion some sort of bomb,” Schiff said.

“We’ve had a number of scenarios since the collapse of the Soviet Union where there have been sales or purported sales,” he added. “This is a concern with us very much today and unfortunately into the future.”

A bomb made of the materials could be devastating, Schiff said.

“Should they get this material and go to Times Square or the financial district, they could render these areas uninhabitable for some time,” Schiff said.

The United States and Moldova have been working together for years to counter nuclear smuggling, said Eric Lund, spokesman for the Department of State’s Bureau of International Security and Nonproliferation.

A joint action plan, approved by both countries in July 2011, aims to improve security at facilities with radiological sources, provide radiation detection equipment, and share best practices against nuclear smuggling, Lund said.

U.S. officials are working with Russian authorities about the smuggling, State Department spokesman John Kirby said.

“I can’t speak to a specific operation or investigation going on, but it is an issue that we routinely talk to Russian authorities about, and as I said, I think we believe is a shared concern between our two governments,” Kirby said.

The sting operations in the eastern European nation were first reported Tuesday by The Associated Press.

Oleg Balan, the Moldovan interior minister, gave these details about three cases in the past five years:

• In July 2010, police seized 1.8 kilograms of Uranium 238, known as yellowcake, in a garage in Moldova’s capital, Chisinau. The uranium was worth €9 million ($10.1 million at today’s rates), but the suspects had tried to sell the uranium for €5 million ($5.6 million). Seven people were arrested, including two officers of the former Soviet army.

At the time, Moldova said it wasn’t sure where the uranium came from.

• In 2011, seven people were caught trying to sell 1 kilogram of Uranium 235 that had come from Moldova’s separatist Transnistria region. The suspects had sold a sample to undercover investigators. One of the suspects escaped, though others were arrested. A year later, an appellate court in Chisinau freed three and sentenced the rest to three to five years in jail.

When uranium is mined, it is 99.3% Uranium 238 and 0.7% Uranium 235, the Nuclear Regulatory Commission says.

Nuclear reactors must have a higher concentration of Uranium 235 than naturally exists in the mined material, so the U 235 isotope is enriched to about 5%, the commission says.

• In February 2015, authorities arrested two Moldovans in the capital on suspicion of trying to sell a half kilogram of radioactive Caesium 135. The arrest came after the suspects sold a sample of 83 grams for €100,000 ($112,440).

Moldovan authorities cooperated with the FBI in all three investigations, Balan said.

The International Atomic Energy Agency says that from 1993 to 2013, 664 incidents of theft or loss of nuclear or radiological materials were reported. It says it doesn’t know how many times these materials were subsequently sold.

CNN’s Jason Hanna and Laura Koran contributed to this report.