Detectives are to probe corruption claims at a firm linked to a council at the centre of "extremely serious allegations".

North Lanarkshire Council launched an investigation last week after its leader received an anonymous letter making making serious claims of corruption at the local authority.

Police Scotland are also looking into the matter and say they are reviewing the claims which centre around contracts and the council's procurement process.

Officers are now looking into separate allegations relating to central heating and electrical firm Saltire, which is one-third owned by the local authority, after the council contacted police about the firm.

A Police Scotland spokeswoman said: "North Lanarkshire Council has made Police Scotland aware of the allegations and the matter will be reviewed."

A spokesman for North Lanarkshire Council said: "The council made Police Scotland aware of an historical piece of correspondence in relation to Saltire which we felt should be examined.

"As this is now a police matter it would be inappropriate to comment further."

Saltire, on behalf of North Lanarkshire Council, is responsible for the maintenance and repair of gas and solid-fuel central heating in the council's housing stock.

Wide ranging allegations were made against North Lanarkshire anonymously by letter to council leader councillor Jim Logue on Thursday.

STV News understands the allegations are "wide ranging" and relate the council's contract tender process. Councillors as well as council officials are understood to be implicated in the claims.

Cllr Logue said last week: "These allegations, which are detailed, concern some of the council's procurement processes. If true, they are extremely serious.

"I immediately instructed Paul Jukes, the chief executive, to launch an investigation. That investigation, led by the council's internal audit team, is already under way. Should the auditors find anything which substantiates these allegations that evidence will immediately be handed over to Police Scotland.

"It is essential that the people of North Lanarkshire are able to have full confidence in the way the council conducts its business and I am determined that we are transparent at all times.

"Although these are currently unsubstantiated, anonymous allegations I believe that it is right to carry out a full investigation and share any evidence which comes to light with the police.

"As that investigation is now under way, it would be inappropriate for the council to comment further‎."