By Mark Trevelyan

(Reuters) -Just as Ukrainian forces are losing their grip on the pocket of Russia's Kursk region they captured last year, they have staged a little-publicised incursion into the adjacent Belgorod region, according to Russian military bloggers.

Several Russian military correspondents said on Friday that Ukrainian troops were inside Belgorod and fighting battles with Russian forces there.

Neither Kyiv nor Moscow has confirmed the reports, though Russia's Defence Ministry said 10 days ago its forces had thwarted five Ukrainian attempts to push across the border in Belgorod.

Ukraine's military has not commented on any thrust into Belgorod region, though that could be for operational security reasons.

Ukrainian President Volodymyr Zelenskiy, addressing reporters in Kyiv, said Ukrainian forces had taken "certain steps" in Russia outside the Kursk region to ease pressure on Ukrainian troops in the area.

Zelenskiy said the action was intended to "reduce the accumulation" of Russian troops and had occurred "a little below the Kursk region." He did not elaborate.

Andrii Kovalenko, an official at Ukraine's National Defence and Security Council, suggested in a March 18 statement that Ukrainian forces could act in the Belgorod region, "neutralising threats" from Russian forces that might mass near the border.

Rybar, a Russian military blog with 1.3 million subscribers, said there had been heavy clashes in a settlement called Popovka and each side was hitting the other with drones. Another Telegram account, Two Majors, said Russian forces were conducting "defensive operations."

"There are constant strikes on concentrations of Ukrainian Armed Forces, but the enemy still has serious offensive potential for this direction and has not abandoned plans for further breakthroughs, including in new areas of the front," it said.

A third military blog, Arkhangel Spetsnaza, reported fighting in a village called Demidovka and said some Ukrainian soldiers were surrounded there.

Reuters could not independently confirm the accounts.

The Ukrainian operation may be an attempt to distract Russian forces as they try to drive out the last Ukrainian forces from neighbouring Kursk. One of the Russian blogs, Rybar, said Russia had moved reinforcements to Belgorod from Goptarovka in the Kursk region.

Emil Kastehelmi, a military analyst with the Finnish-based Black Bird Group, said Ukrainian forces had penetrated the first Russian defences and advanced most likely to a depth of three to four km (1.9 to 2.5 miles).

But he said it was unlikely they could stage a serious breakthrough and threaten any important Russian logistical routes or cities.

"The Ukrainians can, in theory, take some more villages from the border area, but that's not what a breakthrough means - it'd be a small tactical success, but there's very little to be achieved in the Demidovka direction at operational or strategic level," he told Reuters.

"There's no proper element of surprise, and the Russian presence in the area is strong enough to at least conduct mostly successful defensive operations."

In Kursk, the Russian Defence Ministry said on Friday its forces had recaptured the village of Gogolevka, one of only a handful of settlements still held by Ukraine out of around 100 that it seized last August.

Ukraine's General Staff said its military had stopped 18 Russian assaults in Kursk region over the past day.

Open source mapping from Deep State, an authoritative Ukrainian military blogging resource, showed Russian forces in control of some but not all of Gogolevka, and indicated Kyiv's troops still controlled just under 80 sq km (31 sq miles) of Kursk.

President Vladimir Putin visited Kursk this month in a sign of increasing confidence that Russia will shortly win it back, depriving Ukraine of a bargaining chip in future peace talks.

(Additional reporting by Anastasiia Malenko and Tom Balmforth in KyivEditing by Peter Graff and Rod Nickel)