The sudden rise of the well-armed, well-financed and media-savvy Islamic State militant group could not have come about unless unscrupulous companies and individuals slipped money to the group or did business with it, said founders of a new, private research and advocacy group that will seek to expose such dealings and apply pressure to stop them.

“They’ve taken great advantage of modern communications and modern financial techniques” to promote themselves, recruit followers and amass money and weapons, said Mark D. Wallace, a former Bush administration diplomat and lawyer heading the new organization, which will formally launch Monday. “There’s been an absence of people operating to counter that.”

President Obama and other world leaders are making the extremists, who have seized control of large areas of Iraq and Syria since May, a central theme of next week’s annual United Nations General Assembly.

The group, called the Counter Extremism Project, is modeled on United Against Nuclear Iran, the hawkish investigative and advocacy group Wallace also runs here. The two nonprofit groups share some prominent advisers, including former Bush administration Homeland Security adviser Frances Townsend and former Obama administration diplomat Dennis Ross.

The group has compiled detailed financial information about the Islamic State that will be released next week, Wallace said.

It has begun building what it claims will be the best publicly available database of information about extremist groups and their supporters. The information will be provided to governments as well as the private sector, media and other outlets, organizers said.

Many Western diplomats are worried about the group’s apparently flush bank accounts and arsenals, a senior State Department official said. Some of the weapons were seized from the fleeing Iraqi Army, but many others are presumed to be provided to the group by supporters or purchased on the black market. The Islamic State is smuggling oil from seized facilities in northern Iraq and selling it in Turkey, the official said. Turkey has pledged to clamp down on that lucrative traffic, as well as the flow of weapons and foreign fighters across its porous border with Syria.

The official spoke on condition of anonymity because she was not authorized to discuss U.S. intelligence and other assessments of the militants on the record.

Gary Samore, formerly Obama’s top adviser on arms control and weapons of mass destruction, said although it has no power of enforcement, the new group has significant leverage over terror financiers or enablers. The threat of public exposure, with the resulting damage to professional reputations or the risk of prosecution, can stop businesses from making illicit deals or lessen the chances that foreign governments will look the other way, Samore said.

Qatar, Turkey and Saudi Arabia, all U.S. partners against the Islamic State, are among the governments that have failed to prevent private individuals from making donations to the group, current and former U.S. officials said.

“Frankly it’s not that easy to stop these financial transfers. It’s very, very difficult even if the government makes a sincere effort,” said Samore, now executive director of Harvard’s Belfer Center for Science and International Affairs. He is on the advisory board of the new organization.

Wallace would not disclose donors for either United Against Nuclear Iran or Counter Extremism Project. He said support for the new group comes from nonprofit entities and private individuals in the United States and elsewhere, and includes no U.S. or other government money such as foreign sovereign wealth funds.

United Against Nuclear Iran has strong ties to many pro-Israel groups, but the extent of its affiliation is unclear. It has worked alongside the Obama administration in identifying potential sanctions violations but also became a prominent and well-funded skeptic of the current strategy of rolling back sanctions in exchange for negotiated nuclear concessions.

The Justice Department took the highly unusual step of intervening in a civil defamation lawsuit against United Against Nuclear Iran earlier this month. Although the group has no known access to classified government information, the Obama administration argued that a Greek shipper’s subpoena request for the group’s files would jeopardize national security. The shipping magnate seeks its donor lists and financial information gathered about him. The Justice Department cited no precedents for using what is commonly called the state secrets privilege.

The new Counter Extremism Project group is nonpartisan, Wallace said, and is advised by both Republicans and Democrats. It will not seek to supplant the Treasury or State departments or foreign governments in tracking potential sources of support for the Islamic State and other violent extremist organizations, but will supplement and sometimes critique that work, Wallace said.

“The focus of our attention now is ISIS,” said Joseph I. Lieberman, a former senator from Connecticut and another Counter Extremism Project adviser. “They are getting money in different ways, some of it unfortunately by the own means of brutality and criminality, but some of it is dependent on business deals they are making.”