Six Syrians including two infants died of thirst and hunger as they attempted to cross the Mediterranean Sea in a makeshift boat, the UN refugee agency said Monday.

More than thirty people attempted the crossing on the vessel, with many of the survivors in an "extremely serious" state of health according to UNHCR.

"Six Syrian refugees including children, women and teenagers lost their lives at sea. They died of thirst, hunger and severe burns," Chiara Cardoletti, UNHCR official in Italy, wrote on her Twitter account.

"This is unacceptable. Strengthening rescue at sea is the only way to prevent these tragedies," she added.

The victims included two children aged one and two years old, a 12-year-old child and three more adults, including a grandmother and mother also travelling with children who survived the journey, according to a UNHCR statement.

The 26 survivors were being treated in Pozzallo, Sicily.

It was not specified which country they had departed from.

According to the European border and coast guard agency Frontex, the central Mediterranean route was used by more than 42,500 migrants from January to July -- an increase of 44 percent compared to the first seven months of 2021.

UNHCR says 1,200 people have lost their lives in the Mediterranean since the beginning of the year.