(CNN) The United States imposed sanctions against six men for their involvement in human trafficking and smuggling of migrants in Libya in a case first exposed by a CNN undercover investigation .

The US Treasury on Monday announced financial restrictions placed on the six men as a result of reporting from CNN's Nima Elbagir, who documented how the men profited from the smuggling and exploitation of migrants and refugees in a network that spanned Africa.

The US Ambassador to the UN, Nikki Haley, said the images seen in the report of people being sold as slaves in Libya "shocked our conscience."

The US sanctions, which include blocking their assets, come not long after the UN Security Council slapped sanctions on the group last Thursday as part of a Dutch-led initiative, which was also supported by the US, UK, France and Germany.

Alleged traffickers include Libyan Coast Guard official

Four Libyans and two Eritreans are accused of leading criminal networks that traffic vast numbers of vulnerable migrants through Libya to Europe. Strikingly, one of them is a commander with the Libyan Coast Guard, whose efforts to stem the flow of migrants are supported in part by funding from the European Union. He is accused of using firearms to deliberately sink boats carrying migrants.

Another is accused of having longstanding links with ISIS and is known for "cultivat[ing] relationships with terror groups," according to UN documents obtained by CNN.

Others in the group are accused of selling migrants as "sex slaves" and being responsible for some of the worst migrant boat accidents in the Mediterranean.

The motion for sanctions was filed to the UN Security Council's Libya sanctions committee by the Netherlands, supported by France, Germany, the United Kingdom and the United States. It followed a months-long investigation by a panel of UN experts. Russia put a "technical hold" on the motion in May and requested more evidence, but dropped its objection on Thursday.

It's the first time the committee has slapped international sanctions on individuals for human trafficking.

Prosecutors say accused act 'untouchable'

Dutch prosecutors describe the men as ostentatious with their wealth and as individuals who have acted with impunity.

"The sanctioned individuals are young, mostly 30-something, and people who really want to spend their money; on their militia, their business, but also on properties and goods all over the world. They feel untouchable," the Dutch Prosecutor's Office said in a statement.

Dutch Foreign Minister Stef Blok told CNN the sanctioning of the Coast Guard commander "shows that we will go to whatever place or organization concerned in finding and punishing the people responsible, even if it is an organization that we are working together with in other fields."

Documents obtained by CNN show how the men profited from the smuggling and exploitation of migrants and refugees in a network that isn't limited to one part of Africa.

"This abuse has reached an unprecedented scale and level of severity, and these illicit activities have resulted in thousands of fatalities on land and sea," one of the UN documents says. "This cynical business model has enabled armed groups to accumulate vast wealth," it adds.

The sanctions imposed will freeze the six men's financial assets including personal bank accounts and the revenue from their global business activities. The six men will also be subject to strict travel bans.

"These sanctions will help stop the flow of blood money ... It will prevent them from buying protection in Libya which in turn can destabilize the region," the Dutch National Prosecutors' Office said.

CNN contacted those named, where contact details were available, but has not received responses.

Smuggling migrants is lucrative

Each year, tens of thousands of people pour into Libya -- the final transit stop before a short but dangerous sea voyage across the Mediterranean to Europe.

For those involved in the smuggling and trafficking networks , it has been a lucrative and exploitative business with revenues in the billions, according to the European Migrant Smuggling Center (EMSC).

In 2015, migrant smuggling networks made between EUR 4.7 billion ($5.5 billion) and EUR 5.7 billion trafficking people bound for Europe, according to a 2017 EMSC report. There was a sharp decline in 2016, with profits falling by nearly EUR 2 billion from 2015, according to the same report.

Some of those using the central Mediterranean route are refugees fleeing conflict while others are economic migrants.

A crackdown by the Libyan Coast Guard means fewer boats are making it out to sea, leaving the smugglers with a backlog of would-be passengers on their hands. As a result, there are increasing reports of migrants being sold in slave auctions before facing the most appalling conditions.

Migrant testimonies provided to the International Organization for Migration (IOM) have revealed "the image of a Libya in chaos, where violence and abuse are increasingly frequent and armed groups find human beings an extremely profitable source of money."

'The situation is dire'

Last year, CNN reporters went undercover at a slave market in Libya to document the violation of human rights and inhumane treatment that so many desperate migrants have suffered.

"The situation is dire," Mohammed Abdiker, the IOM director of operation and emergencies, told CNN in November. "Some reports are truly horrifying and the latest reports of 'slave markets' for migrants can be added to a long list of outrages."

The evidence filmed by CNN was handed over to the Libyan authorities, who immediately launched investigations into the networks operating in the region.

The footage also sparked international condemnation and a backlash of protests around the world.

On Friday, the UK -- one of the countries that supported the proposal for sanctions -- said it was ready to push for additional sanctions against other human smugglers

In a statement, British Foreign Secretary Boris Johnson said the UK would "work with partners" to "introduce additional sanctions against other individuals who threaten the peace, stability or security in Libya, or who undermine its peaceful political transition."

The co-designating countries highlighted CNN's reporting on Libya's slave trade.

"It was CNN that drove the attention to this terrible slave trade that has been going on in Libya for far too long," Blok, the Dutch Foreign Minister, said.

"As Netherlands is currently a member of the UN Security Council, we proposed to them to impose sanctions on six of the worst perpetrators -- and that will mean that this crime won't be left unpunished."