The British navy has detained seven suspected pirates in the Seychelles, using a team of police dogs to detect the presence of firearms or explosives on their ship, officials said.

"The seven suspected pirates are alleged to have been involved in an attempted act of piracy on a vessel that supplies the Seychelles tuna fleet," the Foreign Office said in a statement.

They were detained by Royal Marines accompanied by a police dog team which found traces of explosives or firearms -- evidence which will help prosecutors in the Seychelles, who have agreed to bring a case against the seven.

"Providing sufficient evidence to convict pirates has been a real problem for the international community as pirates often throw their weapons overboard and claim to be fishermen," the Foreign Office said.

"However, the dog handling team is able to search the suspected pirate vessel for traces of explosives and firearms.

"Rocket-propelled grenades (RPGs) are a weapon of choice for the pirates, but even if they are disposed of in the sea they leave explosive residue that the dogs can identify."