Scotland's biggest police force is investigating the 16th armed raid in its area in two months following the hold-up of security guards at a bank in West Dunbartonshire and a failed heist at a bookmakers in Glasgow.

Scotland's biggest police force is investigating the 16th armed raid in its area in two months following the hold-up of security guards at a bank in West Dunbartonshire and a failed heist at a bookmakers in Glasgow.

Detectives said the latest robbery - at the Bank of Scotland in Alexandria on Monday night - bore striking similarities to previous robberies at four other banks in the Strathclyde area in recent weeks.

Armed attacks have taken place at five banks and eight betting shops in Glasgow, and one in Airdrie, in North Lanarkshire, since the beginning of July.

Armed robbers also struck at a frozen food shop and a sports complex during the same period.

Several robberies of bank or security staff in June in the Glasgow area also remain unsolved.

Strathclyde Police said earlier this week that the volume of robberies over the past two months "was completely unacceptable" and officers were working "tirelessly" to prevent further attacks.

In the latest incident three men wearing balaclavas escaped with a five-figure sum after breaking into the Bank of Scotland in Main Street, Alexandria, as security guards were replenishing an ATM between 9.05pm and 9.45pm on Monday.

The raiders threatened the guards with a bladed weapon before fleeing to a nearby waiting car.

The guards were "extremely distressed" by the incident but were uninjured.

Yesterday, at about 12.05pm a man entered Ladbrokes bookmakers in Trongate, Glasgow, and threatened staff with what appeared to be a firearm before demanding money. He fled empty handed when this was refused.

Last Tuesday robbers made off with a six-figure sum after attacking security guards outside the Bank of Scotland in Kilmarnock Road, Shawlands.

Police believe the robbery was linked to another armed raid on a branch of the bank in nearby Pollokshields at the beginning of August, where more than £100,000 was also taken.

A £10,000 reward has been offered for information leading to the arrest of the suspects.

In two other robberies at banks, a four-figure sum was taken during a raid on a branch of the Royal Bank of Scotland in Glasgow Road, Paisley, on July 19.

Thieves also made off with an empty cash box after targeting the Bank of Scotland in Baillieston Road, Baillieston, less than two weeks later.

The Xscape sports and entertainment centre at Braehead was also targetted in what police described as a "well-planned robbery" last month.

The armed attacks on bookmakers - eight in Glasgow and one in Airdrie -have been described by the trade as an "occupational hazard".

Following Monday night's raid in Alexandria, Detective Inspector David Tassie said: "The robbery bears a striking similarity to previous robberies at other banks in the Glasgow area. However, we have no evidence to link them at present."

A spokesman for G4S (Group 4 Securicor) Cash Services, which delivers cash to more than 90% of ATMs at banks across Britain, said: "We continue to work closely with trade unions, the police, the government and relevant local authorities to develop initiatives to prevent attacks against those working in the cash-in-transit industry."

David Dickinson, chief executive of the British Security Industry Association, said: "The attack in Alexandria is yet another reminder of the serious nature of cash-in-transit robbery.

"Far from being a victimless crime, cash-in-transit attacks are perpetrated against men and women going about their everyday working lives and performing an essential public service."