Eritrea says a British security firm has committed acts of espionage and attempted acts of terrorism and sabotage on its territory.

On December 24, the Eritrean navy detained four British nationals who worked for the British company Protection Vessels International, or PVI.

In a statement Thursday, Eritrea's Foreign Ministry accused the detainees and other PVI personnel of engaging in criminal activities that violated Eritrea's sovereignty. The statement said PVI personnel “invaded” the Eritrean island of Romia last November and conducted tactical military maneuvers.

It said that in December, PVI carried out acts of spying on the island of Harmil and set up an arms depot that included small arms, bulletproof vests and sophisticated radios.

Eritrea said the PVI members, including the four detainees, must be held accountable. It said the legal proceedings on the matter “have not yet been finalized.”

It also said the British government must be held accountable for giving PVI a permit that the company used as a cover for its activities.

There was no immediate reaction from British officials or from PVI.

The detention of the four men has strained relations between Britain and Eritrea. British officials say they have been been denied consular access to the men and that Eritrea has rejected dialogue on the issue.

PVI bills itself as the world leader in armed maritime security. On its website, it says its security teams are recruited exclusively from the British Royal Marines.

The company says it offers safe passage through high-risk transit regions along the east coast of Africa and into the Indian Ocean — the main areas where Somali pirates operate.