Belarus has claimed there was a significant grouping of Ukrainian troops massed near its border and warned that this posed a threat to its security.

"At present, a significant grouping of the Ukrainian army is concentrated in the immediate vicinity of the Belarusian-Ukrainian section of the state border," the defence ministry said in a post on Telegram.

"The probability of armed provocations, which can escalate into border incidents, has been high for a long time," it said, adding that it would take "measures to adequately respond" but would act in a restrained way.

Belarus allowed Russia to use its territory as a launch pad for the invasion of Ukraine a year ago, and President Alexander Lukashenko said last week it was ready to do so again.

Kyiv has voiced concerns for months that Belarus could join the war on Russia's side, a potential threat that has forced it to divert troops to defend the north of Ukraine while waging war with Russia in the east and south.

Mr Lukashenko says Belarus would only enter the war if attacked by Ukraine.

His army has been training with Russian forces for months. Tuesday's statement said more than 150 joint events were planned this year, including a major exercise called "Union Shield 2023" in September.

Reuters was unable to immediately verify the situation at the border, although photos from Chernobyl near the Belarussian border showed Ukrainian serviceman taking part in joint military drills on Monday.

A senior Ukrainian presidential aide said Belarus was stepping up "aggressive and militaristic rhetoric" ahead of the first anniversary of Russia's invasion, but that Kyiv saw no imminent threat from its northern neighbour.

"We do not see any logistics action in Belarus aimed at forming a strike force. Nor do we see the accumulation of equipment needed for a ground offensive," Mykhailo Podolyak told Reuters in response to Belarus's claims.

"Official Minsk is unwaveringly supporting Russia on the information side.

"Nevertheless, we have the northern direction (facing Belarus) under special control."

Belarus's claim comes as Mr Lukashenko announced he had ordered the formation of a new volunteer territorial defence so everyone knows how to "handle weapons" and be ready to respond to an act of aggression and keep public order in peacetime.

"The situation is not easy. I have said more than once: every man — and not only a man — should be able to at least handle weapons," Mr Lukashenko said at the meeting of his Security Council on Monday.

"At least in order to protect his family, if needed, his home, his own piece of land and — if necessary — his country."

He has also said the "experience" in Ukraine necessitates additional defence.

Defence Minister Viktor Khrenin said the territorial defence force will have 100,000-150,000 volunteers, or more if needed.

The paramilitary formation will be ideally in every village and town.

The country's professional army has about 48,000 troops and some 12,000 state border troops, according to the 2022 International Institute for Strategic Studies' Military Balance.

A pariah in the West, Mr Lukashenko, Europe's longest-serving ruler who has led Belarus for 28 years, depends on Russia politically and economically, and Russia's President Vladimir Putin's support helped him survive mass pro-democracy protests in 2020.

The dependence has fanned fears in Kyiv that Mr Putin would pressure Mr Lukashenko to join a fresh ground offensive and open a new front in Russia's invasion of Ukraine.