The Islamic State group has received between $US35 million and $US45 million in ransom payments in the past year, a UN expert monitoring sanctions against al-Qaeda says.
Yotsna Lalji told a meeting of the UN Security Council's Counter-Terrorism Committee that an estimated $US120 million ($A129.8 million) in ransom was paid to terrorist groups between 2004 and 2012.
Kidnapping for ransom "continues to grow", she said, as demonstrated by the money the extremist group calling itself the Islamic State has collected, between $US35 million and $US45 million in the past years.
She said in recent years that al-Qaeda and its affiliates have made kidnapping "the core al-Qaeda tactic for generating revenue".
She pointed to an October 2012 recording in which al-Qaeda leader Ayman al-Zawahri incites militants worldwide to kidnap Westerners.
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Lalji said al-Qaeda in the Arabian Peninsula, which operates from Yemen, received $US20 million in ransom between 2011 and 2013, and al-Qaeda in the Islamic Maghreb, which operates in North Africa, received $US75 million over the past four years.
She said the al-Qaeda-linked extremist groups Boko Haram in Nigeria and al-Shabab in Somalia also "have collected millions of dollars over the past years", and the Abu Sayyaf militant group in the Philippines has received about $US1.5 million in ransom.
According to the al-Qaeda sanctions committee, although the media focuses on international hostages who have generated the largest ransom payments, the vast majority of victims are nationals kidnapped within their own country.
Lalji said terrorist groups either carry out kidnappings themselves or in the case of al-Qaeda in the Arabian Peninsula they work with tribesmen in Yemen who deliver hostages for a fee.
