The new United Nations envoy to Libya Ghassan Salameh voiced his approval of a new effort by Italy to curb the flow of migrants departing North Africa to Europe.

Ghassan Salameh described the cooperation between Tripoli and Rome as a “very constructive” way of dealing with an acute problem.

The former Lebanese culture minister was appointed in June as head of UN operations in Libya.

“It would be absolutely unrealistic to ignore the seriousness of the challenge of irregular migration,” Salameh said after meeting Italian Foreign Minister Angelo Alfano in Rome.

“There are hundreds of millions of them across the world. This is very serious problem.”

“I also believe each country has an absolute right to control its borders and that the best way of doing that is through cooperation with neighboring countries.

“We are on a good track of strengthening cooperation to meet this challenge which is a challenge for all of us.”

The UN envoy’s endorsement however was met with misgivings by human rights groups.

Rights campaigners fear Italy’s focus on strengthening the Libyan coastguard to ensure boatloads of migrants are intercepted before reaching international waters could place thousands of people with a right to asylum at serious risk.

More than 600,000 refugees and other migrants have reached Italy from Libya since 2014.

Italy’s center-left government is under intense pressure from domestic opponents and EU partners to close down the route.

Its navy is providing technical assistance to the Libyan coastguard, which has also been provided with new patrol boats and training by its former colonial master.

Alfano said the cooperation was beginning to bear fruit, in a reference to a more than 50-percent fall in the number of migrants rescued at sea during July, when compared to the same month in 2016.

Italy has also been working to stem migrant arrivals in Libya through better controls on the southern border, cooperation with countries like Niger, Chad and Mali that migrants transit on their way to the Mediterranean and a voluntary repatriation program.

Refugee agencies say Libya is too unstable for any potential refugee to be safely returned there.

There is particular concern over the fate of migrants who end up in the country’s detention camps, where conditions are usually squalid and a lack of regulation means people risk torture, sexual abuse and forced labor.

Alfano insisted the Italian government would not compromise on its commitment to human rights.

“It is not a derby between security and humanity,” he said. But he acknowledged Libya’s migrant holding facilities leave much to be desired.

“Now that we have an opportunity to reduce the fluxes and organize refugee camps in Libya, we have to invest heavily in an international, multilateral humanitarian operation to ensure these camps have an acceptable standard in terms of human rights and every other respect,” Alfano said.

Earlier on Tuesday, a Spanish humanitarian organization agreed to the strict Italian rules about rescuing migrants from smugglers’ boats setting out from Libya.

Representatives from Proactiva Open Arms on Tuesday signed at Italy’s interior ministry a “code of conduct” for such rescues, joining other NGOs which operate rescue ships in the Mediterranean just outside Libya’s territorial waters.

But other rescue groups have refused, including Doctors Without Borders, objecting to such rules as allowing armed Italian authorities aboard.

Also on Tuesday, European Union countries started the process of sending migrants who arrived in Europe via Greece over the last five months back to have their asylum applications assessed there.

EU rules oblige migrants to apply for asylum in the country they first enter. But the rules were suspended as hundreds of thousands of people, many Syrian refugees, entered Greece in 2015.

The European Commission says a number of EU countries have made requests to Greece to return migrants but that Athens must give assurances it has adequate reception facilities for them.

Commission spokeswoman Tove Ernst said Tuesday that the asylum rules were reintroduced in December but “it’s not a full resumption, it’s a gradual resumption.”

Greece’s asylum service says requests have been made to return more than 400 migrants.