Three people who were arrested in connection with a series of shootings and a grenade attack in Delft are to be detained for another 90 days.

A coffee shop, tanning studio, jewellery store and clothes shop came under fire last month, while a hand grenade was thrown at The Future coffee shop. Police believe the incidents, which all took place in the early morning, may be linked to a gangland turf war.

The publicprosecution service revealed on Monday that guns, ammunition and a hand grenade were found in the car of a 40-year-old man from The Hague on June 12. Police stopped the man in Noordwijk, where an emergency order was in force after an outbreak of suspicious fires, and arrested him and his 22-year-old passenger, from Delft.

Police later searched two properties and found a grenade and drugs in one of them. A 30-year-old woman who lived at the property was also arrested.

In April catering trade body Korninklijke Horeca Delft issued a warning that members of the Outlaw Motorcycle Gangs were trying to infiltrate the hospitality sector. However, the organisation said two weeks ago that there was no evidence to link the recent incidents to biker gangs.

Nightclubs in Amsterdam and Rotterdam have also been targeted by gangs who place hand grenades on their doorstep as part of a protection scam. If the owners fail to pay up they are attacked with live grenades or machine-gun fire.