Scotland's police force is not in crisis, and officer numbers are expected to be maintained at current levels, the First Minister has said.

Police Scotland is facing a £21m shortfall in running costs this year, despite an £18m budget boost from the Scottish Government for 2016/17.

The Scottish Police Federation (SPF), representing rank and file officers, has already launched a high-profile campaign against cuts to the service.

It claims cost-cutting measures have already seen officers sent to charity shops to buy equipment, while some investigations into drug dealers were being shelved to avoid overtime costs.

Police officer numbers fell to their lowest level for more than five years between April and June, although the number remains well above 2007 levels at 17,242 full-time equivalents.

The SNP dropped its pledge to maintain 1000 extra officers earlier this year.

Asked about a "crisis" in the force at a press conference in Edinburgh, Nicola Sturgeon said: "I don't think the single force is in crisis.

"We work with the police and the Scottish Police Authority to make sure that we have got policing in this country that is appropriate to the needs of this country."

On the prospect of cuts to officer numbers, she added: "Police officers in Scotland are office holders, their terms and conditions are set out in statute, police constables cannot be made redundant in Scotland. That is the legal position.

"So this idea that there is threat of redundancy to police is not true.

"We have, of course, protected police numbers at 1000 above the number we inherited, and the justice secretary very recently has made it clear to the chief constable that is the position we expect them to maintain.

"Like all parts of the public sector right now, of course there are challenges around public spending and we work with public authorities to make sure these challenges are handled appropriately and handled in way that protects frontline services, and that will continue to be the position with the police as well."

The Scottish Liberal Democrats said government "centralisation" had impacted on frontline services.

The party's justice spokesperson Liam McArthur MSP said: "The SNP claim they have protected police numbers. The reality is that their centralisation programme has taken officers off the streets and put them into control rooms and other back office functions.

"The 50% cut in resources for policing we have seen in some areas since 2011 is not going to help officers and police staff keep us safe."