(Makes clear story is an update)
* NATO says working with Italians to clarify facts
* Agency says dozens of migrants appear to have died (Adds NATO spokeswoman, U.N. rights statement)
ROME/BRUSSELS, Aug 5 (Reuters) - Italy called on NATO on Friday to launch an investigation into reports that alliance units failed to rescue migrants fleeing Libya this week when their boat ran into difficulties.
Italian coast guards rescued more than 300 migrants on Thursday from the boat that had been drifting off the Mediterranean island of Lampedusa for several hours.
According to Italian media reports, NATO air and naval units had been aware of the boat but had failed to come to its aid.
NATO said it had been told by Italian authorities that they were responding to the incident. It said it was working closely with them to clarify the facts.
The International Organisation for Migration (IOM) said on Friday that dozens of African migrants appeared to have died of dehydration and hardship on the boat and their bodies thrown overboard, based on accounts from survivors.
“Regarding the controversy over the alleged failure to rescue boats fleeing Libya with illegal immigrants on board, Foreign Minister (Franco) Frattini has asked the Italian representative to NATO to seek a formal investigation into what happened,” the Italian Foreign Ministry said in a statement.
It added that Italy would ask for a discussion within the alliance about whether NATO’s mandate in Libya should be adapted to include the protection and rescue of migrant boats.
NATO spokeswoman Carmen Romero said NATO’s maritime command was told by Italian maritime authorities on Thursday of a distress call from a ship.
“NATO subsequently confirmed with Italian authorities that they had responded to the incident with three ships as well as with helicopter support,” she said.
“Facts of the incident are still emerging and we are working closely with Italian authorities to fully clarify the matter.”
In May, NATO denied a report that alliance units failed to help a drifting boat carrying African migrants from Libya that ran into trouble and led to the death of 62 people from thirst and hunger.
Romero said the 28-nation alliance, which includes Italy, was committed to help those in distress at sea and had responded to incidents in the Mediterranean in March and July.
The IOM said the 20-metre vessel had left from near Tripoli on Saturday, vastly overcrowded with migrants from Nigeria, Ghana, Ethiopia, Sudan, Chad and Morocco, and lacking water and food. It is the latest in a wave of arrivals since NATO states began a military campaign against Libyan ruler Muammar Gaddafi.
The office of U.N. High Commissioner for Human Rights Navi Pillay expressed deep concern at the deaths at sea of so many people trying to reach Europe from Libya and called on “relevant authorities” to take steps to prevent this.
“We also support full inquiries into any cases where necessary assistance was reportedly not provided by naval units in the vicinity with the ability to conduct rescues,” it said.
Hundreds of people have died or drowned attempting the dangerous crossing from North Africa to Lampedusa, a tiny island off the southern coast of Sicily, as fighting in Libya has brought down previously strict border controls.
Earlier this week Italian coast guards found the bodies of 25 men on another boat crammed with African migrants. The men had apparently died of asphyxiation
NATO has 17 ships in the Mediterranean enforcing an arms embargo on Libya and hundreds of planes enforcing a no-fly zone and conducting air strikes on the country.
(Reporting by Catherine Hornby in Rome, Stephanie Ulmer-Nebehay in Geneva and David Brunnstrom on Brussels; Editing by Elizabeth Fullerton)