Along the muddy sidelines of a Warsaw railway, armed guards and a soldier embark on a morning patrol, monitoring the area for strange activities and checking train tracks for signs of sabotage.
Their work is a part of "Operation Horizon", launched by Poland earlier this month to boost rail security and protect critical infrastructure following a series of mysterious incidents which Warsaw blames on Moscow.
Poland a NATO and EU member has become the main hub for transporting Western military and humanitarian support to Ukraine as it fights off an invasion launched by Russia in 2022.
That has sent Warsaw's ties with Moscow into a tailspin and Poland blames Russia for what it says are multiple incidents of sabotage, including drone incursions and arson attacks, which the Kremlin angrily denies.
Earlier this month Polish Prime Minister Donald Tusk blamed "state terrorism" by Russia for two incidents of rail sabotage.
The first incident involved a steel obstruction placed on a track, "likely intended to derail a train", he said.
The second consisted of the detonation of a military-grade explosive device as a freight train passed along a railway crucial to delivering Ukraine aid.
No one was injured in either event. However, Polish Foreign Minister Radoslaw Sikorski warned that the diversions "could have caused a train disaster and the death of many people".
He added that this was avoided "only by a miracle".
Unwilling to leave things to chance, Warsaw has now directed up to 10,000 troops from several different units, including Special Forces, Cyber Defence, and Territorial Defence Forces to help keep an eye on the railways.
"Operation Horizon" will use advanced drones and off-road vehicles equipped with thermal imaging and night vision to watch for trouble, according to the spokesman for the Railway Security Guard.
That includes "unusual behaviour of bystanders near railway areas, unattended items, and interference with railway infrastructure elements," spokesman Pawel Kuskowski told AFP.
Special attention is being paid to "obstacles placed on tracks", he added.
At a train station on the outskirts of Warsaw, nervous passengers admitted the patrols did not ease all their fears.
Grazyna, a 60-year-old retiree who did not wish to provide her last name, told AFP that although she feels safer than before the patrols began, "whether it is completely safe remains uncertain".
Jan Malicki, a 19-year-old pharmacy student, said that he feels less safe since hearing about the sabotage even taking into account the increased security measures.
"You can't be sure if similar incidents won't happen," he said.
Both passengers emphasised that they would continue taking the train. But the air of unease is hard to dispel.
Polish prosecutors have named two Ukrainians allegedly working for Moscow as suspects in this month's incidents of rail sabotage.
They are believed to have fled to Belarus another neighbour of Poland and a close ally of Moscow and on Friday a Polish court issued a warrant for their arrest.
Meanwhile security forces are encouraging passengers to report anything unusual.
"Our soldiers will check every signal," Senior Corporal Przemyslaw Luszczki from the 18th Capital Territorial Defence Brigade told AFP.
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