Four people detained on suspicion of espionage and sabotage

"These are subsequent arrests in the investigation into the activities of an organized criminal group whose task is to commit acts of sabotage, in particular arson, at the request of Russian secret services," the ABW said.

The men have been charged with participation in an organised criminal group and committing acts of sabotage or terrorism on behalf of foreign intelligence.

The suspects are Kamil K., Andrei B., and Stepan K. They face up to life in prison.

The Russian embassy in Warsaw did not immediately respond to a request for comment. Moscow has previously dismissed allegations of involvement in such sabotage.

Poland says its role as a hub for military and other supplies to Ukraine has made it a target for Russian spies who are trying to gather information on support for Kyiv's effort to repel Russia's invasion, as well as engage in acts of sabotage.

A 26-year-old Ukrainian man is suspected of encouraging a Polish citizen to share the photos and "take part in the activities of foreign intelligence", a spokesperson for the minister coordinating the security services said.

The Ukrainian man, named as Oleksandr D., sent messages to a Polish citizen encouraging him to help foreign intelligence, spokesperson Jacek Dobrzyński said.

"This activity was to consist of sharing photos of military vehicles that were intended to help Ukraine and crossed the Polish-Ukrainian border," Dobrzyński said.

"In exchange for the information provided, the Polish citizen was to receive a remuneration of 15,000 euros."

A court agreed to a request to hold the suspect in pre-trial detention for three months. If found guilty he could face up to eight years in prison.