Countries that pay tens of millions of dollars in ransom money to free hostage held by the Islamic State and other terrorist groups are violating UN Security Council resolutions, a member of the UN's al Qaeda monitoring team said Monday.

UN expert Yotsna Lalji told the Security Council's Counter-Terrorism Committee that the Islamic State — also known as ISIS or ISIL — has received between $35 and $45 million in ransom payments this year alone. Between 2004 and 2012, countries, companies, and individuals paid an estimated $120 million to groups that the UN considers terrorist organizations.

Those payments, typically carried out in secrecy, violate a series of Security Council resolutions, Lalji said. In a 2009 measure targeting al Qaeda and its affiliates, the Council made clear that "the payment of ransoms" is prohibited.

Similar language was reaffirmed in resolutions passed in 2011 and 2012, and again in a high-profile resolution voted through at the behest of the Obama administration during this year's General Assembly in September. The most recent resolution used even stronger language, saying ransom payments to blacklisted groups are prohibited "regardless of how or by whom the ransom is paid."

But payments nevertheless continue, and are believed to have bought the freedom of several European hostages held alongside Steven Sotloff, James Foley, and Peter Kassig — Americans beheaded by the Islamic State this year. The militant group disseminated graphic videos of the killings online, generating public outcry that led the Obama administration to expand American bombing campaigns against the Islamic State and other extremist groups in Syria.

William Braniff, executive director at the University of Maryland's National Consortium for the Study of Terrorism and Response to Terrorism, told VICE News that even though the US refuses to pay cash for hostages, American military involvement in Syria and Iraq offers the Islamic State another form of currency.

'We don't know how many back room deals have been made with European countries or companies.'

"It's really important to understand that terrorism is part of a larger political conversation," Braniff said. "It may be they [the Islamic State] need funding, and hostage taking is one way to meet a pragmatic requirement, but they might also need legitimacy on the world stage. Trying to beat a foreign power into intervening in the conflict is one way to gain that legitimacy."

Reports by the New York Times and others have implicated several European countries, including Germany, France, Austria, Italy, and Switzerland in ransom payments made to the Islamic State, and to al Qaeda-affiliated groups in Africa and Asia. European countries have denied making ransom payments, but experts see no other explanation for the release of their citizens.

At the Security Council, Lalji referenced a 2012 audio message from al Qaeda chief Ayman al-Zawahiri that urged the group's followers to kidnap Westerners. Kidnapping, Lalji said, is now "the core al Qaeda tactic for generating revenue."

Lalji said al Qaeda in the Arabian Peninsula (AQAP) earned $20 million from hostage taking between 2011 and 2013. The Yemen-based arm of the terrorist group reportedly pays local tribes to snatch victims. Al Qaeda's North African affiliate reportedly received some $75 million worth of ransom payments over the past four years.

"The Europeans have, in essence, created a very perverse incentive," Mia Bloom, professor at the University of Massachusetts Lowell's Center for Terrorism and Security Studies, told VICE News. "We don't know how many back room deals have been made with European countries or companies."

Braniff, however, pointed out that the European countries that pay ransoms are likely considering the safety of individual citizens, with less concern about how the money may fuel a larger conflict.

The US invasion of Iraq is typically cited as the genesis of the Islamic State, which was formerly known as al-Qaeda in Iraq. The UK — a US ally during the Iraq war — also refuses to pay ransoms to release its citizens. The militant group beheaded British citizens David Haines and Alan Henning earlier this year.

"An Italian politician may see hostages as a casualty in somebody else's war, so they want to extricate themselves from that any way they can," Braniff said. "Whereas the US feels a much greater stake in the outcome of the current conflict."

"There's no value judgment about who's right or wrong, but there's a different history leading to that hostage being taken and that ransom being demanded," Braniff added.

Earlier this month, the Obama administration reviewed its hostage policy, but officials remain adamant they will not budge and start paying ransoms.

"The United States has set a heartrending but absolutely necessary example by refusing to pay ransom for captured Americans," Secretary of State John Kerry said last week.

The Islamic State has reportedly demanded a $6 million ransom for its last remaining American hostage, a 26-year-old female aid worker.

But foreign aid workers and reporters in Iraq and Syria have become more vigilant or cancelled trips entirely in recent months, potentially making hostages — and the controversial ransom payments that have sown distrust among Western allies — less of a dilemma going forward.

With US-led airstrikes targeting the oil infrastructure thought to generate millions of dollars worth of revenue for the Islamic State, the group could step up pressure on locals to meet its funding needs. The UN says these local communities already bear the brunt of kidnappings and extortion by the militant group.

"The extortion goes from 'pay us protection money,' to 'if you're not going to pay us, give us one of your kids,'" Bloom said. "It's a very coercive atmosphere."