Twelve people have been arrested after dawn raids across the North West - including at properties in Oldham.
Nine men aged between 22 and 54 have been arrested - along with three women aged 25 to 34.
All are being questioned of conspiracy to supply drugs, money laundering and firearms offences.
Warwick Road and Medlock Road in Failsworth were among properties targetted.
Police have said in a statement: "This morning police executed eight warrants across Manchester and Merseyside.
"Warrants were executed as part of Operation Brooks - set up by GMP to target an organised crime group believed to involved in the supply of drugs and possession of firearms and grenades across the region.
"Warrants were issued at properties on Falside Walk and Pirie Walk in Newton Heath, Warwick Road and Medlock Road in Failsworth and Parkview Road, Parkhill Road and Camelford Road in Liverpool."
Inspector Anthony Norman from GMP's Serious and Organised Crime Group said: "Thanks to the dedication and professionalism of our officers, we have been able to apprehend a large group of individuals this morning.
"I'd like to thank colleagues in Merseyside who have assisted us with today's operation.
"Our enquiries remain ongoing and I'd encourage anyone with information to contact us.
"The best weapon we have against drug dealers is the wider community, on whom we rely to help us catch and prosecute those who seek to profit from the sale of narcotics."
Anyone with information should contact police on 101 or the independent charity Crimestoppers, anonymously, on 0800 555 111.
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