A cohort of special agents were on board a boat that capsized in Italy's Lake Maggiore on Sunday.
Officials in northern Italy named Claudio Alonzi, 62, and Tiziana Barnobi, 53, as the Italian security agents who perished when the boat sank after a violent storm appeared over the lake.
Another fatal victim was Shimoni Erez, 50, a former member of the Israeli security forces.
Russian national Anya Bozhkova, 50, was also killed aboard the boat - which was piloted by her husband.
Initial reports said there were a number of Brits on the houseboat, but information about their injuries is yet to be shared.
On Sunday, the 52ft-long boat sank after a "small hurricane" developed over the lake, dragging the 25 people on board - who were celebrating a birthday - into the icy waters.
The incident happened between the towns of Sesto Calende and Arona at around 7pm on Sunday night.
Divers searched into the early hours of Monday morning to recover the bodies of the two missing passengers.
Of the 25 on the boat, the majority managed to swim ashore between the towns of Lisanza and Piccaluga. Some were rescued by other boats.
Two people were taken to hospital in "moderately critical" condition, three were taken in "not very critical" condition and 15 were treated at the scene and did not need to be taken to hospital.
Seven ambulances, an air ambulance and several medical vehicles raced to the scene.
Video from the lake shows chairs and other debris from the boat floating in the water.
The alarm was raised by another boat that saw passengers in the water, La Repubblica reports.
Lake Maggiore is the second-largest lake in Italy and a popular destination for British tourists.
The President of Lombardy Attilio Fontana said in a statement: "Unfortunately there is news of some missing people. A whirlwind caused a very serious accident.
"The firefighters of the Milan diving unit are at work on the spot together with the guard coast, to the air rescue and to the ambulances of Areu.
"I am following with apprehension the updates of the rescue teams on the spot which I thank ".
The whirlwind was part of a storm system that hit Lombardy Sunday evening, forcing delays at Milan's Malpensa airport.
According to local reports, the vessel was a "house-boat" and not a sailing ship as was originally reported.
The group of passengers had gone out onto the lake to celebrate a birthday in the afternoon, but the weather turned deadly as they approached close to Arona at around 7pm.
The ship couldn't stay afloat and tipped over, throwing everyone into the water.
Fourteen of them swam to nearby Piccaluga, where they were rescued by emergency responders waiting there.
Five of them were taken to hospital, three of them with minor injuries, and two in moderate condition.
