More than 700 firearms have been seized and 74 people arrested in Britain after a massive European operation targeting blank pistols, the UK's National Crime Agency said Sunday. 

The arrests and seizures are part of an international investigation launched five years ago involving Spain's Guardia Civil police force, Europol and authorities in other European countries, the National Crime Agency (NCA) said in a statement. 

The operation targeted alarm or blank pistols which can be modified to become lethal weapons.  

"Each of these 700 firearms had the potential to fall into the wrong hands and be used by criminals to further their offending or, at worst, take a life," said Charles Yates, deputy director of the National Crime Agency. 

While these blank weapons are authorised in several European countries, it is forbidden to import and possess them in Britain. 

"Criminals like the guns because they are cheap, resemble firearms such as Glocks so can be used to intimidate or threaten others, and they can be converted into lethal weapons," the NCA said. 

The majority of the weapons seized were intercepted at Britain's borders, before they could be used, he added. 

The Spanish Guardia Civil police force had identified suspicious purchases of blank-firing weapons by foreigners before tracking them down and intercepting them.