Tests are under way to establish what type of explosive was used in Monday's Armier boathouse bomb and how the attached mobile phone detonated it, according to sources.

In the meantime, the police continue to probe all possibilities, including whether the bomb was aimed at one or both of the two men who found it and whether it went off because it had been mishandled. Pierre Cremona, 40, from Tarxien, and William Farrugia, 31, from Qormi, escaped unhurt on Monday night after what is known as an improvised explosive device went off in the terrace of Mr Cremona’s boathouse at Torri l-Abjad at about 11.30pm.

The two men reported that the blast occurred soon after they noticed a small box wired to a mobile phone in an unused oven among other items on the terrace.

They said they took action as soon as they spotted the device and dashed towards their cars, driving away just in time.

They also told the police that a black van, with two men inside, which had caught their attention earlier in the night, was nowhere to be seen after the explosion.

The mobile phone attached to the explosive device, which was recovered by members of the Armed Forces of Malta’s Explosive Ordnance Disposal, is central to the investigation.

The sources said further forensic tests were required to establish whether the device was set off remotely, possibly using another mobile phone, or whether the phone was used as a timer.

Chemical tests are also being held to find out what sort of explosive material was used.

Preliminary inquiries have established that the device was capable of causing severe if not fatal injuries at very close range.

The sources said the device was similar to the one placed under the pick-up truck belonging to Paul Degabriele from Fgura a year ago.

That device did not go off, though Mr Degabriele was shot dead in Marsa on March 31.