"Our two organizations strongly condemn this and any attack on civilian life," the UN refugee agency UNHCR and the UN migration agency, the International Organisation for Migration said in a joint statement.
"We also call for an immediate end to detention of migrants and refugees. We call for a guarantee of their protection in Libya," it said.
The air raid late on Tuesday, apparently carried out by forces loyal to the warlord Khalifa Haftar "deserves more than condemnation", the statement said, demanding "a full and independent investigation...to determine how this happened and who was responsible, and to bring those individuals to account".
Besides at least 44 people who were killed, 130 people had been severely injured" in the attack, according to the UN's Libya mission.
"For that reason, we expect the final death toll to include many more victims," the statement underlined.
"We also call for an immediate end to detention of migrants and refugees. We call for a guarantee of their protection in Libya," said the statement.
The statement noted that the IOM and UNHCR had already warned of the perils of returning migrants and refugees to Libya after their interception in the Mediterranean by Libyan coastguard under a European Union backed policy.
"Including those victims at Tajoura, some 3,300 migrants and refugees remain arbitrarily detained inside and around Tripoli in conditions that can only be described as inhumane," the statement stressed.
"Moreover, migrants and refugees face increasing risks as clashes intensify nearby. These centres must be closed," it said.
The UNHCR had already called in May for the Tajoura centre, which holds 600 people, to be closed after a previous air strike injured two migrants detained there and damaged its roof.
( With inputs from IANS )