Six Syrian migrants, including three children, died while trying to cross the Mediterranean Sea to Europe.
The UN High Commissioner for Refugees (UNHCR) said 26 rescued migrants who arrived in the Sicilian port of Pozzallo said the bodies of six people had been left at sea.
A merchant ship had rescued the migrants, mainly Syrians and Afghans, from a small boat in distress off the Libyan coast.
"They died of thirst, hunger and severe burns," Chira Cardoletti, UNHCR's representative to Italy, wrote on Twitter.
"This is unacceptable. Strengthening rescue at sea is the only way to prevent these tragedies," she added.
According to a UNHCR statement, the victims were three children -- aged 1, 2, and 12 -- and three adults. Another 26 survivors, many in an "extremely serious" condition, were brought to Sicily and taken into care in Pozzallo, it added.
A child with dehydration and his mother were also transported to the Maltese capital of Valletta by helicopter.
The agency says that at least 1,200 people have lost their lives in the Mediterranean Sea since the beginning of the year. Several hundred migrants have also been rescued in recent days by humanitarian NGO ships.
More than 600 people are currently waiting to disembark the vessels Sea Watch 3 and Humanity1 after being rescued in the Mediterranean.
According to the European agency Frontex, the central Mediterranean migration route to Italy has been used by more than 42,500 migrants from January to July this year. That represents an increase of 44% compared to the first seven months of 2021.
The Turkish coast guard said on Tuesday that it had rescued 73 other people trying to reach Europe off the coast of the southwestern province of Mugla. Ankara has accused Greece of illegally pushing migrants back.
"Greece denies any involvement in the alleged fatal incident," Greek Migration Minister Notis Mitarachi wrote on Twitter.