President Vladimir Putin has ordered stronger border security to ensure "fast" Russian military and civilian movement into Ukrainian regions now under Moscow control.
Speaking in a congratulatory message to the border service, a branch of Russia's Federal Security Service (FSB), on their Border Guard Day holiday, Putin said their task was to "reliably cover" the lines in the vicinity of the combat zone.
Attacks inside Russia have been growing in intensity in recent weeks, chiefly with drone strikes on regions along the border but increasingly also deep into the country, including on an oil pipeline north-west of Moscow on Saturday.
"It is necessary to ensure the fast movement of both military and civilian vehicles and cargo, including food ,humanitarian aid building materials sent to the new subjects of the (Russian) Federation," Putin said in a message posted on the Kremlin's Telegram messaging channel.
Kherson, Zaporizhzhia, Luhansk and Donetsk are the four regions in Ukraine that Putin proclaimed annexed last September following what Kyiv said were sham referendums. Russian forces only partly control the four regions.
On Saturday, officials said three people were injured in Ukrainian shelling in Belgorod, a region that was the target of pro-Ukrainian fighters this week that sparked doubts about Russia's defence and military capabilities.
The Kursk and Belgorod Russian regions bordering Ukraine have been the most frequent target of attacks that have damaged power, rail and military infrastructure, with local officials blaming Ukraine.
Kyiv almost never publicly claims responsibility for attacks inside Russia and on Russian-controlled territory in Ukraine, but said that destroying infrastructure is preparation for its planned ground assault.
Ukraine indicated on Saturday that it was ready to launch along-promised counter offensive to recapture territory taken by Russia in the 15-month long war, a conflict that has claimed the lives of thousands and turned Ukrainian cities into rubble.
Drone attack
Two drones damaged an administration building of an oil pipeline in Russia's western Pskov region, the regional governor said Saturday.
The explosion is the latest in an escalating series of attacks in Russia amid the Ukraine offensive.
"Early morning, an explosion damaged the administrative building of the oil pipeline near Litvinovo, Nevelsky district," governor Mikhail Vedernikov said.
Shortly after, he said that, according to preliminary information, the building was "damaged as a result of an attack by two unmanned aerial vehicles."
There were no reported casualties, and an investigation was still ongoing.
The blast took place in the village of Litvinovo, around 10 kilometres (6.2 miles) from the Belarusian border.
Unconfirmed reports from Baza, a Russian Telegram outlet with sources in the secret services, said the drones were targeting the Transneft oil pumping station in Pskov.
Baza also reported an attack targeting an oil refinery near Erokhino, in the western Tver region.
The Tver region press service said a drone had crashed near Erokhino without injuring anyone, but did not give any more details.
Over the past few weeks, reports of drone attacks in Russia have multiplied, usually in regions bordering Ukraine.
On Friday, two drones damaged buildings in the centre of the southern Russian city of Krasnodar, which had been relatively unaffected.
Moscow has blamed Kyiv -- and its Western supporters -- for the escalating number of attacks and sabotage operations, including on the Kremlin.
Ukraine has denied involvement.
The regional governor of Belgorod said on Saturday that his region had come under fire again, a day after reporting dozens of Ukrainian strikes.
There were no casualties in the shelling, which hit Shebekino, around seven kilometres (four miles) from the Ukrainian border, governor Vyacheslav Gladkov said.
This week, the region saw an unprecedented two-day incursion from Ukraine, with Russia using troops and artillery to put it down.
Reuters and Agence France-Presse