Some 60 survivors have been rescued and brought to shore in the coastal town of Al-Khoms, around 100 km east of Tripoli, said the UNHCR statement.
A search and rescue operation by Libyan Coast Guard and local fisherman is continuing and UNHCR teams are giving survivors with medical and humanitarian assistance, the statement said.
"We must not simply accept these tragedies as inevitable," said Vincent Cochetel, UNHCR Special Envoy for the Central Mediterranean.
"Sympathies must now become actions that prevent loss of life at sea, and prevent the loss of hope that motivates people to risk their lives in the first place."
Following Tuesday's tragedy, some 900 people have perished trying to cross the Mediterranean to reach Europe this year, according to UNHCR.
UNHCR called on the European Union to re-deploy its Sophia migrant search and rescue vessels in the Mediterranean after the bloc suspended its naval mission in March. UNHCR also urged an end to "legal and logistical restrictions" (placed by Italy) on charity search and rescue boats and planes.
"Coastal states should facilitate, not impede, voluntary efforts to reduce deaths at sea.
"These measures should go hand in hand with increased evacuation and resettlement places from states to move refugees in Libya out of harm's way," UNHCR said.
Over 4,800 refugees and migrants are currently being held inside facilities in Libya, UNHCR said.
During a visit to the war-torn North African country on Tuesday, UNHCR's Deputy High Commissioner for Refugees, Kelly Clements, underlined the agency's commitment to working with Libyan authorities on alternatives to the arbitrary detention of boat migrant who are returned there, the UNHCR said.
( With inputs from IANS )