Maltese police have arrested one of the country's most prominent businessmen in connection with an investigation into the murder of journalist Daphne Caruana Galizia.

Yorgen Fenech was detained after police intercepted his yacht off the Mediterranean island, sources with knowledge of the matter said.

His arrest came the day after the government said it would offer a pardon to a suspected middleman in the 2017 murder of Ms Caruana Galizia if he provided legal binding evidence of who was behind the killing.

Mr Fenech is a director and co-owner of a business group that won a large energy concession in 2013 from the Maltese state to build a gas power station on the island.

His luxury yacht Gio left the Portomaso yacht marina, 8km north of Valletta, shortly before dawn. Police swiftly boarded the vessel and forced it to return to port.

In February 2017, eight months before she died in a car bomb, Ms Caruana Galizia wrote in her blog about a mystery company in Dubai called 17 Black Limited, alleging it was connected to Maltese politicians, without publishing any evidence.

She was unable to discover who owned the company. A Reuters investigation later identified Mr Fenech as the owner.

According to a December 2015 email, uncovered by Maltese financial regulators, secret Panama companies owned by then Energy Minister Konrad Mizzi and Keith Schembri, the government chief of staff, stood to receive payments from 17 Black for unspecified services.

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The email said the Panama companies expected payments of up to $2 million within a year from 17 Black. 

The email made no reference to the gas power station and there is no evidence any money was deposited with them.

Mr Schembri and Mr Mizzi both told Reuters last October they had no knowledge of any connection between 17 Black and Mr Fenech, or of any plan to receive payments connected to Mr Fenech or the energy project.

Mr Fenech denied making any plans to pay any politician or any person or entity connected to them.