Russia is ramping up pressure on civilians in occupied parts of Ukraine, according to Ukrainian officials, whose forces have stepped up their assaults behind enemy lines ahead of a widely expected counteroffensive.
The assault could prove a critical opportunity after 14 months of war, not just for Ukraine to regain territory but also for it to try and persuade its Western allies to send still more weapons and aid. Anticipating the campaign, and still recovering from their costly and stumbling winter offensive, many Russian forces have shifted into defensive positions.
Despite its staggering losses, Russia still controls a large swath of Ukrainian territory. But Ukrainian forces have repeatedly struck Russian positions far from the front, and on Tuesday the Russian authorities reported more shelling and — for the second day in a row — an explosion that derailed a freight train in the Russian border region.
The Russian authorities in occupied territory, wary of strikes by Ukrainian partisans and special forces, have imposed strict new measures on civilians. Most recently, they have “reinforced” counterintelligence units and are restricting travel between towns and villages, Ukraine’s military high command said Tuesday.
Last week, the Kremlin decreed that anyone in occupied territory who did not accept a Russian passport could be relocated from their homes, an edict that has sown confusion and fear among residents, according to the Ukrainian military and local officials.
Undercover Russian security officers have also started working in crowded public spaces to track down members of the Ukrainian resistance, according to the National Resistance Center, a Ukrainian government agency.
The plainclothes officers often initiate conversation “to find ‘disloyal’ citizens,” the agency warned. Ukrainians who “take the bait are forced to continue to collaborate with the Russian occupation regime,” it said.
It is virtually impossible to independently verify much of what happens in Russian-occupied territory, because independent journalists, humanitarian groups and international observers are rarely granted access by the Russian authorities.
But the Kremlin has made no secret of its efforts to absorb the regions into Russia.
Even before President Vladimir V. Putin announced in September the annexation of four Ukrainian provinces, a move widely condemned as illegal, Russian forces enacted measures to Russify the internet and other elements of daily life like school curriculums and currency.
Ukrainian officials typically call on people who live in occupied territories to resist Russia any way they can, but they have offered mixed advice on how to respond to the recent pressure. While the Ukrainian human rights commissioner urged people to get Russian passports for their own safety, a deputy prime minister advised against taking them.
Serhii Khlan, a deputy administrator of the Kherson Regional Council, told Ukrainian television late Monday that there was “enormous” pressure on the local population. He said people were worried they would be considered “collaborators” if they accepted passports.
Civilians in once-occupied areas have described torture and abuses by the Russian authorities, and an atmosphere of intense fear and paranoia about who may be working with the Russians and who may have ties to the Ukrainian military or special forces.
Russia has accused Ukraine of carrying out attacks far behind the front line. Ukrainian officials usually refuse to confirm or deny responsibility, but say they reserve the right to strike places used as staging grounds for attacks on Ukraine. Under this rationale, Ukrainian forces have periodically hit targets inside Russia.
In the Bryansk region early Tuesday, a village less than five miles from the border with Ukraine came under shellfire, the third straight day of explosions in the area. The shelling started a fire, but there were no casualties, the regional governor, Aleksandr V. Bogomaz, said on Telegram. He blamed the Ukrainian military, though the claim could not be independently verified.
Later in the day, the Russian railway operator said on Telegram that about 20 cars of a freight train had derailed because of the “illegal interference” of “outside” actors — the second derailment reported in the region in two days.
“An unidentified explosive device went off in the area of the Snezhetskaya railway station,” Mr. Bogomaz said.
On Sunday, he said four people in the region were killed by Ukrainian shelling. And on Monday, an explosion caused a freight train to derail in the region. The governor blamed an unidentified explosive device, and the country’s rail service said “an intrusion by unauthorized individuals” led to a fire.
In March, Ukrainian special forces said they had destroyed an unmanned observation tower in Bryansk, and partisans claiming to fight for Ukraine made an armed incursion into a village there, leading to emergency measures from the Kremlin.
Victoria Kim contributed reporting from Seoul.