The tension flare-ups just keep coming in the armed confrontation between Ukraine and Russia and now the military buildup at the borders has reached the most dangerous level in two years.

This is a bad one. The latest showdown has caused Western capitals to fear Russian President Vladimir Putin might be about to launch a whole new battle with Ukraine that would be just the start of a deeper armed conflict.

The situation escalated last week when Moscow accused Ukraine of sending sabotage teams armed with explosives into the Crimean peninsula, which Russia seized from Ukraine and formally annexed in 2014.

Kiev dismissed the Russian allegations as "fantasies" designed to provoke a new border war.

But Putin added fuel to the fire by describing those alleged sabotage missions as terror attacks that killed two Russians, a soldier and an FSB security officer.

"This is a very dangerous game," Putin insisted on state television. "There is no doubt we will not let these things pass."

'Repelling saboteurs at sea'

In subsequent meetings with his top military brass, Putin reportedly reviewed "scenarios for counterterrorism security measures along the land border, offshore, and in Crimea airspace."

​ A missile corvette fires during the Navy Day celebrations in Sevastopol, Crimea, on July 31. The Kremlin has ordered its large Black Sea Fleet based in Crimea to hold immediate war games. (Pavel Rebrov/Reuters) Russia has all it needs for a major show of force. It has been increasing its forces along the edge of eastern Ukraine throughout the summer and can mobilize 40,000 soldiers with heavy armour and local air support. It also just added its most advanced s-400 missile air defence system, which has a 400-kilometre range.

On Thursday, the Kremlin ordered its large Black Sea Fleet based in Crimea to hold immediate war games to practise "repelling saboteurs at sea."

Thoroughly alarmed, Ukraine put all its troops along the border with Crimea and the eastern border zone facing Russia on the highest state of combat readiness.

As the stakes continued to rise, many countries were left trying to figure out if there's any truth to Russia's allegations.

Moscow's evidence of the attacks is limited to a brief video of some explosive materials that were seized and an arrest — Kiev insists the suspect is an abducted civilian.

Russia says more evidence will follow. It alleges on the night of Aug. 6/7, a group of Ukrainian commandos slipped across the border into Crimea with explosives meant to sabotage the local economy and tourist sites, but they ended up killing a Russian security officer in a firefight.

Two nights later, Moscow alleges, Ukrainian artillery launched "massive fire" over the border into Crimea to try to cover a second sabotage attack. The sabotage mission failed, but the attack killed a Russian soldier, the Kremlin says.

A member of the self-proclaimed Donetsk People's Republic (DNR) walks past a house damaged by shelling in the eastern Ukrainian city of Donetsk on Nov. 29, 2015. (Alexander Ermochenko/Reuters) Kiev, on the other hand, says Russia's story is simply a stunt to give Putin an excuse to provoke major new fighting by pro-Russian rebels in Ukraine's disputed eastern sectors.

It's a tricky situation for diplomats because neither Moscow nor Kiev is considered above exaggeration or outright fabrication. Also, in some border areas, Kiev doesn't always have control of the many private militias that might pursue sabotage campaigns on their own.

Whatever the truth, there remains widespread suspicion that Putin is quite happy to increase tensions with Ukraine for a mix of political and diplomatic goals.

It certainly wouldn't take much to once again enflame the disputed eastern regions of Ukraine, where 10,000 people have been killed in 2 ½ years of fighting and the shaky truce of the Minsk II agreement seems to be crumbling.

Both sides consistently violate the ceasefire, with hundreds of infractions including artillery, mortar and sniper fire every week.

Teams of international observers meant to patrol the peace are routinely threatened at gunpoint and blocked by Ukrainian military, or more often by Russian-backed rebels.

Putin's motives

Longtime observers of Putin seem to agree he's fuelling the tension for all it's worth, but they differ over his motives.

Well-known as a skilled, high-stakes opportunist in foreign matters, some believe Putin wants to scare the West into dropping some sanctions against Moscow when international talks about Ukraine resume in September.

"We're looking at a classic Russian strategy of building up tension," Mark Galeotti, a Russian expert with New York University, told the New York Times.

He said Putin is determined to enter any future talks in a strong position.

An escalating showdown with Ukraine could present political benefits for Putin. (Alexander Zemlianichenko/Reuters) "And the only real strength is to say, 'I could make things much, much worse if I wanted to.'"

It's also an interesting time for Putin to pressure the West given the European Union is still reeling from Britain's Brexit referendum and the U.S. is preoccupied with a somewhat bizarre election in which the Republican candidate seems a fan of Putin.

Putin may also welcome a new crisis atmosphere to rally support for the party he founded, United Russia, in September's parliamentary elections. The party remains his power base, but its popularity has declined slightly because of the country's slumping economy. Putin's popularity and that of his party usually rise during an international crisis.

The concern, of course, is no one knows how intense the latest showdown may become. Even if Putin isn't interested in anything more than localized skirmishes and heavy-handed displays of force, there are obvious dangers with keeping nerves on edge.

One such danger is that the forces facing each other in these contested border regions are better armed than before, with enormous lethal force capabilities on both sides.

The other danger is that conflicts in all parts of the world these days have a greater tendency to break loose and spread their venom far and wide.