Kidnapping of aid workers has become "big business" as militants often work with crime networks to carry out abductions, a senior United Nations official and former hostage said on Tuesday.
Vincent Cochetel, who was held captive in Chechnya in 1998, said countries must bring kidnappers to justice to stem a steep increase in attacks, which are undermining aid operations.
"We need to absolutely get the perpetrators to court," Cochetel, who works for the U.N. refugee agency (UNHCR), told the Thomson Reuters Foundation, adding that it was usually possible to trace many of those involved.
"These people can be tried any time, anywhere, and they can be extradited, so it's important to make sure that when those individuals are known everything is done to bring them to justice."
Last year 130 aid workers were abducted, up from 45 in 2007, according to the Aid Worker Security Database, which records attacks on aid workers. High-risk countries included Afghanistan, the Democratic Republic of Congo and South Sudan.
Kidnapping is a longstanding problem in Afghanistan, either for ransom or to put pressure on Western governments, while rebels in South Sudan have carried out mass abductions of humanitarian convoys to control aid delivery.
Most kidnap victims are national staff, held on average for 12 days, according to database research in 2013. International staff are usually held for longer as demands for money or concessions are often steeper.
Cochetel, who spent 317 days in captivity, said attacks were increasing as militants teamed up with criminal organizations to form hybrid groups, which saw kidnappings as "part of their business model."
Aid agencies and most governments do not pay ransoms, he said, but payments are sometimes made by third parties such as businessmen with connections to the country where a hostage is being held.
Although kidnapping aid workers is a crime under international law, it is rarely punished, which is fueling the violence, Cochetel said.
Even if hostage-takers cannot be held to account because they live in an area outside state control, states should hit them with travel bans and freeze their assets to stop them benefitting from their crimes and to deter others, he said.
Cochetel was working as head of the UNHCR office in the Russian republic North Ossetia when he was ambushed by armed men outside his flat.
Blindfolded and stuffed in a car boot, he was driven to Chechnya where he was kept handcuffed to a bed in darkness.
The kidnapping was ordered by Chechen militants but outsourced to criminals, said Cochetel, now UNHCR special envoy for the Mediterranean.
Three "small fish" were jailed afterwards, but he knew of few other cases where hostage-takers had faced justice.
Aid agencies have boosted security in recent years, but it eats into resources that could be spent on assistance, and armed escorts and fortified offices create a distance between aid workers and the people they are trying to help.
This can fuel mistrust, and consequently increase security risks for staff, said Cochetel who saw the problems first-hand in Chechnya.
"For some (of the population) it was not clear who we were.
We spent so little time in the places we were visiting because we were scared for our own security," he said.
"It was (a case of) go visit, deliver assistance, go back to the base, sleep in the bunker. And after some time you develop ... submarine syndrome. You don't understand the broader landscape around you."
Cochetel said the UNHCR spent about 2% of its budget on security, but many smaller organisations could not afford to take the same measures - and even seemingly safe interactions could pose risks.
Earlier this year some colleagues were attending a cultural event with women leaders in southeast Niger when two female "dancers" blew themselves up.
Cochetel also called for more help for hostages following their release, including medical, psychosocial and financial support.
He said many were abandoned by their former employers, particularly if their contract had ended during their captivity or they had to stop working because of trauma.
"I'm aware of many ... people who were dropped by their organizations. Some fell into depression, some even took their lives," he said.