Libya's UN-backed government said on Thursday it was investigating the reports of slave trading that have caused international revulsion, promising to bring any perpetrators to justice.

UN Secretary-General Antonio Guterres has been among world leaders expressing horror after footage broadcast on CNN of the bidding and sale of migrants seeking a better life.

Guterres has called for an immediate investigation into the reported sale of African migrants in Libya, saying the transactions may amount to crimes against humanity.

Thousands of African migrants make the dangerous journey to Libya hoping to survive the often deadly crossing of the Mediterranean to Europe. They cite high unemployment and even the changing climate in their often-arid nations as reasons to make the perilous journey.

"There have been direct instructions issued to form an investigative committee so as to uncover the truth and to capture the wrongdoers, and those responsible, and put them before the judiciary," Libyan Interior Minister Aref al-Khodja told journalists in Tripoli. "We are now currently waiting for the results of the investigations which I believe are coming to a close."

A migrant carries a baby at a naval base after they were rescued by Libyan coastal guards in Tripoli on Thursday. (Ismail Zitouny/Reuters)

As they have before, Libyan officials have stressed they are overwhelmed by the numbers taking advantage of their location across from southwestern Europe.

"We, in Libya, are victims of illegal migration and we are not a source for it," the statement said, appealing to foreign powers to help stop flows from migrants' countries of origin and across Libya's southern borders.

This summer, Italy pledged to help Libyan officials to patrol the seas off their coast.

Though sea arrivals to Italy are down almost a third this year, this week was marked by a surge in rescues after several days of bad weather, and one body was recovered, Italy's coast guard and humanitarian groups said. On Wednesday, 1,100 migrants were rescued from 11 boats, the coast guard said, and more than 200 were picked up on Thursday.

Meanwhile, Interpol said Thursday 40 people were arrested and 500 people rescued after a swoop on human trafficking across West Africa. The international police organization said 236 minors were included in the total rescued in simultaneous operations across Chad, Mali, Mauritania, Niger and Senegal.

"The results of this operation underline the challenge faced by law enforcement and all stakeholders in addressing human trafficking in the Sahel region," said the operation's co-ordinator Innocentia Apovo.

Those arrested face prosecution for offences including human trafficking, forced labour and child exploitation.

Rwanda offers help

Rwanda is offering to host some, perhaps thousands, of the African migrants in limbo in Libya.

Rwanda "cannot remain silent when human beings are being mistreated and auctioned off like cattle," the government said, adding that the small East African nation "may not be able to welcome everyone but our door is wide open."

Indeed, Rwanda's political philosophy & the experience of many Rwandans for many years not having a country they call home, have led this country to feel for refugees, migrants,stateless persons...For <a href="https://twitter.com/hashtag/Africans?src=hash&ref_src=twsrc%5Etfw">#Africans</a> being sold in Libya: <a href="https://twitter.com/hashtag/Rwanda?src=hash&ref_src=twsrc%5Etfw">#Rwanda</a> is small, but we will find some space! <a href="https://t.co/5Yf95Bdulj">https://t.co/5Yf95Bdulj</a> —@LMushikiwabo

The statement didn't say how many migrants might be welcome, but the chairman of the African Union Commission said Rwanda has offered to resettle up to 30,000 or transport those who wish to return to their home countries.

The chairman, Moussa Faki Mahamat, urged other African governments and private individuals to "pool resources and add the voices to support our brothers and sisters suffering" in Libya.

"Rwanda is small, but we will find some space!" Rwandan Foreign Minister Louise Mushikiwabo tweeted Wednesday. Her country for nearly a quarter-century has been recovering from its own tragedy, the 1994 genocide that left around 800,000 people dead.