Inadequate naval patrolling means ever more migrants from Africa and the Middle East will die trying to cross the Mediterranean, aid agencies warned on Tuesday, as Italy appealed for a "more vigorous" European response to tackle the crisis.

In the latest tragedy involving migrants, 29 people died of hypothermia on Monday on the exposed deck of a small Italian naval vessel after it rescued them in rough seas from a dinghy adrift near Libya.

The incident has reignited criticism of Italy's decision last year to end a full-scale search-and-rescue mission, known as Mare Nostrum, due to concerns over costs.