Russian forces menace Ukraine, amid Belarus violence

"What we see along our border is a sophisticated military infrastructure ... ready to be used for offensive operations," Ukrainian foreign minister Dmytro Kuleba also told European newspapers on Monday.

They spoke after Russian forces grouped near the Russia-occupied Donbas region in east Ukraine last week, according to Ukrainian military sources and US intelligence.

A new attack felt "more likely" now than it did in April, when Russia last concentrated forces in the region, a Ukrainian security source told this website.

Any military operation in Donbas would be harder in winter, with temperatures already reaching minus seven degrees Celsius.

But Russia-proxy fighters did once capture the Ukrainian city of Debaltseve in a January offensive.

And low-intensity fighting was continuing as usual in Donbas, where international monitors recorded over 700 ceasefire violations a day last week and two Ukrainian soldiers died.

The US secretary of state and French foreign minister also raised the alarm on Sunday by speaking of "concerning" Russian manoeuvres.

"There were reports of [Russian] military movements, regroupings, and probably reinforcements with additional forces, but being done discreetly, mostly at night", an EU diplomat said.

The earlier troop surge in April was mostly a Kremlin "PR exercise", but Russia left in place significant military resources, the diplomat noted.

And the latest alarm bells on Ukraine added to an existing emergency on the EU and Nato's eastern flank.

Two more people also died in the Belarus-Poland border crisis this weekend - a Syrian man found in a forest and a Polish soldier in a firearms accident, bringing the number of victims to 10.

Belarusian soldiers tore down Polish fences to help migrants break through in groups of 50 or more, according to Polish press agency PAP.

They also threw stones at Polish soldiers and armed migrants with tear gas to fire at Polish guards, it said.

"We are discussing with Latvia, and especially with Lithuania, whether to trigger Article 4 of the Nato treaty," Polish prime minister Mateusz Morawiecki told PAP on Sunday.

"Now we need concrete steps and the commitment of the entire alliance," Morawiecki said.

Article 4 entitles Nato members to call snap talks with allies.

The last time it was invoked in Europe was when Russia invaded Ukraine in 2014.

Meanwhile, Poland has already sent 15,000 soldiers to the Belarus border area. Ukraine has sent more than 8,500 to its Belarusian frontier in case the same happened there.

Bad cop, good cop

And for his part, Belarus president Alexander Lukashenko dialled up his war talk.

Weapons had been smuggled to the Polish border from Donbas for false-flag attacks, he said.

And Russia should install nuclear-capable 'Iskander' missiles in Belarus to counter Nato, he added in Russian magazine National Defence on Saturday.

"I need several [Russian] divisions in the west and south, let them stand [there]," Lukashenko said.

He also denigrated international concern by playing ice hockey on TV the same day.

Russia has denied the Ukraine troop build-up reports.

Russian president Vladimir Putin also denied earlier Polish accusations he had masterminded the Belarus migrant skirmishes.

And he offered an olive branch on Sunday by putting off a Black Sea military drill.

"There is no need to further add to tensions there," he said on TV.

But Poland was not alone in seeing the Ukraine and Belarus threats as part of a coordinated Russian effort to destabilise its Western-allied neighbours.

The mixed-format attack was accompanied by a Russian squeeze on EU and Ukrainian gas supplies, Kostiantyn Yelisieiev, a former Ukrainian presidential aide and EU ambassador, also told EUobserver.

"The Kremlin's way of thinking is complex and dangerous. It is multidimensional," Yelisieiev said.

Winter is here

Temperatures likewise fell below zero on the Belarus-Poland border this weekend, where thousands of people, including women and children, remained at risk.

EU foreign ministers, meeting in Brussels on Monday, were expected to blacklist Belarusian officials and entities for "trafficking" them there from the Middle East and forcing them to attack Europe's borders.

Turkish Airlines said it would stop selling tickets to Belarus under threat of future EU sanctions, but was still flying to Minsk on Sunday.

Syria's Cham Wings cancelled flights, Russia's Aeroflot denied flying in migrants, and Belarusian carrier Belavia said it would stop services from Damascus.