Greek police believe a mechanical fault may have caused a helicopter to crash moments before it was due to land on the island of Sifnos, killing a British couple on their honeymoon and the pilot.

Authorities were focusing on Tuesday on a "strange noise" the aircraft reportedly made before falling to the ground and exploding on impact. The helicopter was a privately chartered Bell 206.

"We can confirm that two passengers, Marie Ebert and Alexander Cromie, died in the incident on Monday evening," a police officer said.

Ebert and Cromie, both London-based and aged 30 and 31 respectively, had chosen Sifnos for their honeymoon after recently marrying.

Officials in Syros, the Aegean's administrative centre, identified the pilot as Giorgos Raikos, 53, describing him as a former air force officer and "extremely experienced."

One well-placed source said: "The focus of the inquiry is now on the helicopter and possible engine failure. What has happened is nothing short of a tragedy."

The deputy mayor of Sifnos, Manolis Fountolakis, told Greek television: "People in the area have testified hearing the helicopter making a noise, a strange noise, probably a mechanical fault in the air and because the propeller was doing something strange."

CCTV footage of the aircraft spiralling out of control as it approached the island's helipad near the village of Exambela is also being studied by investigators.

A local resident, Antonis Zambelis, was quoted as saying: "The helicopter crashed about 50 metres away from houses with people inside and about 50 metres from the landing spot next to the Panayia tis Vrysis monastery."

Thick plumes of smoke engulfed the crash site after the helicopter ignited in a fireball. Rescue workers who scrambled to douse the flames subsequently discovered the remains of all three victims.

Greece's Ministry of Infrastructure and Transport was coordinating the inquiry on Tuesday as senior law enforcement officials converged on Sifnos.

The island's mayor, Maria Nadali, said: "We are shocked and are trying to manage, together with the right services, the consequences of this incident next to the helipad."

Hiring private helicopters has become increasingly popular in Greece, with tourists chartering them to travel between islands in the Ionian and

Aegean seas. Once considered remote, Sifnos lies approximately 120 miles (195 km) south-east of Athens and takes several hours to reach by ferry.