"We can no longer afford to ignore what's happening inside Libya," UNHCR spokesperson Charlie Yaxley told Euronews.
The United Nations has condemned the deadly shooting of three Sudanese migrants in Libya.
UN agencies reported on Tuesday that three migrants had been killed near the western coastal town of Khoms after they were intercepted by the coastguard in the Mediterranean Sea and returned to shore.
The three were among more than 70 Europe-bound migrants, who were returned to Khoms late on Monday, said Safa Msehli, a spokesperson for the International Organization for Migration (IOM).
The IOM said local authorities started shooting when the migrants attempted to escape from the disembarkation point. Two others were reportedly wounded and taken to local hospitals while survivors were moved to detention.
Two of the migrants died at the scene and a third died of their injuries while being transported to a hospital, according to the UN refugee agency, UNHCR.
Charlie Yaxley, UNHCR spokesman, told Euronews the organisation had called for an urgent investigation.
"We can no longer afford to ignore what's happening inside Libya," said Yaxley.
"We need to take greater steps to ensure nobody is returned there after being rescued at sea and greater action is needed to support the human rights network in the country."
Euronews has attempted to contact the UN-supported Libyan government and the coastguard for a statement.
Most migrants in Libya attempt to make the perilous journey to European shores in ill-equipped and unsafe rubber boats.
The IOM said earlier this year its estimated death toll among migrants who tried to cross the Mediterranean passed the "grim milestone'' of 20,000 since 2014.
In recent years, the European Union has partnered with the coast guard and other Libyan forces to stop the flow of migrants.
Rights groups say those efforts have left migrants at the mercy of brutal armed groups or confined in overcrowded detention centres that lack adequate food and water.
"This is not the first time people are subjected to this senseless violence and confirms yet again that no one should be returned to Libya,'' Msehli said.
The EU agreed earlier this year to end an anti-migrant smuggler operation that involved only surveillance aircraft and instead deploy military ships.
In 2019 a leaked EU report found that the bloc had spent more than 90 million euros funding and training the Libyan Coast Guard over two years.
But the report also suggested that the EU's ability to monitor the coast guard's activity was limited.
In an April debate in the Civil Liberties Committee, MEPs further insisted that Libya is not a “safe country” for disembarkation, adding to UN calls for the EU to stop channelling funds to the country.
"Any support that is given by other states to Libyan entities must be made conditional on an improvement in the human rights situation there and must be monitored," Charlie Yaxley told Euronews.
"If it does not, such support should be halted".
Click on the player above to watch Alex Morgan's report in #TheCube.