LVIV, UKRAINE (NYTIMES) - Two weeks after Mr Valeriy, an actor and amateur photographer, settled in western Ukraine after fleeing his home in Kyiv, he was stopped and questioned by the local police.

Someone had reported him as he strolled around the city photographing its squares, churches and other landmarks - many now buttressed with sandbags.

The police officers took him to their car and scrolled through the recent photos on his mobile phone, leafed through his sketchbook, and checked what channels he subscribed to on the social messaging app Telegram.

"They were even reading my memes to check if I am making fun of us or them," he said, meaning Ukrainians or Russians. Luckily for him, the officers found a meme of ragtag Russian soldiers with televisions for heads - an allusion to the intense propaganda Moscow is churning out - and let him go.

Mr Valeriy, 32, who asked that his full name not be used for fear of recriminations, is not alone in having to look over his shoulder. With Russia's full-scale invasion of Ukraine now into its second month, suspicion has settled like a fog over the country, joining anger and unity as the dominant emotions.

Ukrainians have been shaken by reports of "dyversanti" - saboteurs and diversionary groups working for Russia who mix into the civilian population, sow confusion and mistrust, and possibly even alert the enemy to potential targets. Civilians who were already living in fear are seeing spies everywhere.

"With this level of anxiety, and trying to find sources of danger, the more you imagine things when you don't know what the beast looks like," Mr Valeriy said.

Suspicions run particularly high in Lviv, near the Polish border. Because it has been largely spared the destruction and horror of cities farther east, it has become a magnet for ukrainians seeking safety, as well as a transit point for those headed to Poland. As such, its population has grown temporarily by up to 400,000, local officials say.

That has put a lot of unfamiliar faces on Lviv's streets, and raised the antennae of those who live there permanently.

In the first weeks of the war, police and administrators fielded more than 17,000 calls a day about supposedly suspicious activity, Lviv's regional governor Maksym Kozytsky said in an interview. Now law enforcement bodies are fielding about 10 per cent of that volume, he said. But that is still more than 1,000 a day.

Police officers and members of the Territorial Defence, a volunteer unit of the Ukrainian army, patrol the streets of Lviv and check cars at roundabouts. Men serve at checkpoints on the entrance to every city or village nearby, reserving the right to check documents.

There are legitimate reasons for suspicion. During the first month of the war, Ukraine's intelligence agency, the SBU, dismantled 20 saboteur groups and apprehended 350 more saboteurs, a spokesman, Mr Artem Dekhtiarenko, said last week.

And Mr Kozytsky wrote on his Telegram channel that Saturday (March 26), a day when Russian missiles struck two industrial facilities in Lviv, police had stopped a suspicious car and checked the phones of the two men inside. He said they found videos and photos showing the movements of Ukrainian military.

"They also had photos of the passports of men with Luhansk registration and many contacts with Russian numbers," he said.

The assertions could not be independently verified.

Ukrainians of all stripes have tried to help authorities in any way they can. Patriotic, militaristic music blares from the speakers of every restaurant and cafe. The Italian protest song "Bella Ciao" has been recast in Ukrainian with lyrics celebrating the donated American-made Javelin missiles and Turkish Bayraktar drones being used by the troops.

And ordinary civilians can join the fight by reporting suspicious activities. An app, eVorog, a wordplay that means "there is an enemy," asks people to report any suspected military activity. It has received more than 200,000 submissions in a month, according to the Patrol Police, a subdivision of the police responsible for public order.

The perception is that while Russian forces cannot send their armies to surround Lviv, the enemies - individuals and small groups who can blend in with the other hundreds of thousands of outsiders - are already within.

A law enforcement official, who declined to be identified because of the tense atmosphere in the city, pointed out that Ukraine and Russia have been fighting for eight years in the East. He shared stories of recent apprehensions of saboteurs posing as humanitarian workers.

"Of course they have had time to carefully prepare," he said.

A 10pm curfew is in effect, though the streets are mostly empty by nightfall. Mysterious messages get passed around warning that the Russians plan to target representatives of western embassies or aid agencies that have moved from Kyiv.

Previous attacks in the West were also supported by local assets.

An amateur aviator from Lutsk, north-east of Lviv, where the military airport was hit twice, had been providing information to Russian security services since at least 2017, the SBU found after detaining the man recently. They accused him of communicating with the Russians about the activities of the military during the first week of the war.

"People are enraged," said Mr Ihor Polishchuk, the mayor of Lutsk. "The person who was detained had posed as a civic activist," he said, adding that the man's arrest had "increased the level of suspicion of possible spies."

The SBU reported similar instances of assistance in attacks on the military airports in the cities of Ivano-Frankivsk and Vinnytsia.