Vladimir Putin accuses Ukraine of killing Russian servicemen in terrorist attacks in Crimea and warns that the deaths will not be ignored. The Ukrainian president, Petro Poroshenko, orders his country’s military to be in a state of combat readiness. Talks over the Minsk agreement, which established a ceasefire of sorts in the vicious conflict, have been put on hold. There are dire predictions that Ukraine is sliding back into war.

The upsurge of this particular episode of violence, and its venue, has come as a surprise. There has been low intensity, but rising, strife in separatist Donetsk and Luhansk in the east over the last few months, but Crimea has not experienced serious military action since it was annexed from Ukraine by the Kremlin in the chaotic aftermath of the Maidan protests.

That is not to say that Crimea has been entirely calm. Tartar and Ukrainian activists had claimed systematic persecution by the Russian dominated government in Simferopol. Some of those we met while reporting from there at the time have fled, some are in prison. On the Ukrainian side of the border pipelines carrying electricity into the peninsula have been blown up, creating severe power shortages: groups of Tartars have blocked roads at the de-facto border, stopping supplies from getting in.

Inside Story - Is the conflict in Ukraine about to escalate?

The reason for the timing of this flashpoint remains unclear. Some of us covering the fighting in eastern Ukraine were surprised that the Russians consented to the first Minsk agreement before taking the city of Mariupol which would have helped open a land corridor from the Donbas to Crimea. The Azov Sea port was vulnerable at the time: most of the Ukrainian forces had withdrawn and its defence was reduced to a few hundred increasingly disillusioned fighters from nationalist militias.

Eastern Ukraine, despite periodic flare ups, has been a frozen conflict since then; a state of affairs which should suit Moscow. No one seriously believes that Crimea, which was part of Soviet Russia until 1954, would ever revert to Ukraine. Kiev, backed by the West, continues to claim suzerainty, but the Ukrainian government also admits that it cannot make that happen by military means.

Russia’s opponents hold that the Kremlin has always wanted to reactivate military action and what better time to do that than when world attention is distracted by the Rio Olympics? Mr Putin, they repeatedly point out, has form for this; the war between Russia and Georgia took place in 2008 at the time of the Beijing Olympics.

But there is evidence that on that occasion it was Mikheil Saakashvili who had begun hostilities by sending troops into the rebel enclave of South Ossetia, albeit he may have fallen into a well-prepared Russian trap by doing so. The Georgian president had believed that the US would come to his aid if necessary, despite a senior American diplomat warning him this would not happen. In the event we saw the American forces training the Ukrainians head off fast to Tblisi airport along the George W Bush Boulevard when the fighting started.

Moscow has claimed that an officer in its intelligence service, FSB, and a Russian soldier were killed in two separate fire fights at the weekend. It is also claimed that weapons, including explosives for 20 bombs, and grenades, intended for use in an insurgency campaign, have been discovered.

“A terrorist ring” has been broken up, and one of those arrested, say the FSB, is Evgeny Panov, a 39-year-old agent of Ukrainian military intelligence (GUR). The authorities in Kiev confirmed that he was a Ukrainian citizen but refused to make any further comments for “data protection reasons”. President Poroshenko described the charges as “absurd and cynical” and “a pretext for the latest military threats against Ukraine”.

But are the Russians really preparing for military operations against Ukraine from Crimea? Those of us there at the time of the Russian takeover in 2014 were convinced that a plan already in place was in play. A demonstration in the capital, Simferopol, was followed by soldiers in unmarked uniform, the “little green men”, seizing strategic locations; marine infantry from the Russian Black Sea fleet quickly surrounded Ukrainian bases while the government in Kiev dithered.

This time the Ukrainian forces, some trained by the West, are prepared. And, more importantly, it makes little logistical sense for the Russians to carry out an invasion, needing armour, through one bridge and very few crossing points across the isthmus. An amphibious assault would be a massive and risky undertaking. The Donbas remains the logical point of any further intervention, but would the Kremlin even contemplate another military mission with no discernible geo-political advantage while still heavily engaged in Syria?

The Ukrainians themselves are divided over what will happen next. Pointing to Russian military build-up in Crimea Col Andriy Lysenko, spokesman for the presidential administration, maintained that a new offensive could take place next. But Anton Gerashchenko, an MP and advisor to interior minister Arsen Avakov, who is notably hawkish towards Moscow, declared “ I can say openly that we do not anticipate war by the Russian Federation on Ukraine in the near future… Putin’s strategy relies on bargaining with Ukraine over the return of Donbas provided that we abandon all attempts to ever regain Crimea.”

Even Ukrainian military intelligence, accused by Moscow of plotting terrorism in Crimea, seems to be relatively relaxed. Vadim Skibitsky, its spokesman, said the Russian movements were in preparation for an annual exercise, Kavkaz-2016 (although he also pointed out that a Russian exercise was held just before the Georgia war) and added that fresh Russian troops in the Dzhankoy area are part of a regular six monthly rotation.

The EU and US have extended sanctions against Russia over Crimea and the Donbas, but some European states want to see them relaxed in the future. But the Ukrainian government has also been accused of failing to fulfil some of its obligations under the Minsk agreement, such as holding local elections in the areas it holds in the Donbas. Furthermore, there continues to be irritation in the West over the failure of the Poroshenko government to combat widespread corruption.