Ukraine has denied Russian claims that a border raid led to the deaths of five people.
Earlier today Russian news agency Tass reported that a "sabotage and reconnaissance group from the territory of Ukraine" had crossed the border and all members had been killed.
The news service claimed that two infantry vehicles crossed into Russia and that both were also destroyed.
Ukrainian officials have now denied these claims, and said that its forces are not in Rostov.
The Russian press service reported: "On February 21, 2022, at about 06:00 Moscow time, in the area of the settlement of Mityakinskaya in the Rostov region, on the section of the state border of the Russian Federation with the Republic of Ukraine, the border detachment of the FSB of Russia discovered the penetration of a sabotage and reconnaissance group.
"As a result of the clash, five violators of the border of the Russian Federation from the sabotage and reconnaissance group were destroyed."
The claims follow on from an announcement by Russia's FSB security service that a shell fired from Ukrainian territory had completely destroyed a border guard post in Rostov, but caused no casualties.
Ukraine denied responsibility for the incident.
The RIA news agency shared video footage published by the FSB, which showed that a small outhouse had been torn apart.
The footage did not show the projectile.
Ukraine said it had not shelled Russian territory. Its military has previously accused Russia of faking pictures of shells to make out they were Ukrainian, and said that mercenaries have arrived in separatist-held eastern Ukraine to stage provocations in collaboration with Russian special forces.
As tension between the two countries continues to rise, the claims of Ukrainian aggression may be seen as a means to justify retaliation by the Russians.
Today Boris Johnson's spokesperson said that Vladimir Putin's plan to launch an invasion of the neighbouring country had already began.
They said: "The intelligence we are seeing suggests that Russia intends to launch an invasion and that President Putin's plan has already begun.
"We're seeing seen elements of the Russian playbook that we would expect to see in certain situations, starting to play out in real time."
Foreign minister Liz Truss today said that the UK is stepping up preparations with allies for the worst case scenario in the Ukraine crisis, adding that a Russian invasion was highly likely.
"Diplomacy must be pursued but a Russian invasion of Ukraine looks highly likely. The UK and allies are stepping up preparations for the worst case scenario," she said on Twitter following talks with NATO Secretary General Jens Stoltenberg in Brussels.
"We must make the cost for Russia intolerably high."
Last week Russia claimed that it was moving forces back from the Ukrainian border.
Hope that a conflict may be averted quickly evaporated when it became apparent that there were still at least 150,000 troops in the region.
Now Putin has signed a decree to call up army and secret service reservists, which could see tens of thousands ordered into uniform.
