Neil Buckley wrote in his blog for Financial Times.
Keep an eye on Transnistria, the pro-Russian breakaway state in Moldova. On Monday, Dmitri Trenin, one of Russia's best-known foreign policy analysts and a man with good Kremlin antennae, tweeted: "Growing concern in Moscow that Ukraine and Moldova will seek to squeeze Transnistria hard, provoking conflict with Russia." On Tuesday, a columnist in the pro-Kremlin Izvestia newspaper warned that Russia "seriously faces the prospect of a repeat of the  situation" - when it went to war with Georgia - "this time around Transnistria".
What sparked the tensions was a May 21 vote in Ukraine's parliament to suspend military co-operation with Russia. That included a 1995 agreement giving Russia military transit rights across Ukraine to reach Transnistria, which borders Ukraine's Odessa region.
Russian peacekeepers have been deployed in the unrecognised statelet since its brief war for independence from ex-Soviet Moldova in 1992, and Russia has a base there with about 1,350 soldiers and heavy weapons. Losing access via Ukraine means Russia must resupply its base by air through Chisinau, the Moldovan capital, and across Moldovan territory.
But Moscow complains Moldova has recently detained and deported several Russian soldiers. Mr Trenin alleged to the FT, moreover, that Ukraine had deployed S-300 air defence systems near the border.
Cue claims by Russian and Transnistrian officials that Ukraine and Moldova are imposing an economic blockade; civic leaders in Transnistria last week appealed to Russian president Vladimir Putin to protect them "in case of emergency". On Monday, Dmitry Rogozin, Russia's hard-line deputy premier, assured Transnistria's leadership that "Russia will always be there" to ensure regional security.
A senior Ukrainian foreign ministry official insists there is no Transnistria blockade, only a "political decision to suspend military-technical-co-operation with Russia because of Russia's aggression against Ukraine. This is a matter of principle for us."
It is for Moscow, he adds, to ensure in talks with Chisinau that its soldiers have access. He calls any suggestion that Ukraine might try to shoot down Russian planes resupplying its Transnistria base "absurd".
There have been false alarms around Transnistria before since the Ukraine crisis broke out. Its leaders appealed to Moscow to join the Russian Federation days after Russia annexed Crimea, but nothing came of it. About one-third of the region's 500,000 inhabitants are Russians and almost another third are Ukrainians. Some 97 per cent voted in a 2006 referendum to join Russia, which Moscow has never recognised.
But Russian and Transnistrian officials are making more of the issue this time. Transnistria's foreign minister Nina Shtanski alleged on Monday that Ukraine had placed troops along the border - which Kiev denies. And Ukrainian president Petro Poroshenko's unorthodox appointment at the weekend of ex-Georgian president Mikheil Saakashvili - a bête noire for Moscow - as governor of the Odessa region has added an element of psycho-drama.
At least two Russian newspapers speculated on Tuesday that Mr Saakashvili's task was to maintain the "blockade" of neighbouring Transnistria, and even act as "provocateur" to start a new war. The Izvestia columnist suggested that "the fate of all the issues that exist between Russia and the west is being decided today in the Kiev-Donetsk-Odessa triangle".
"This is not only the state TV narrative. Serious people are concerned about the implications of Ukraine's moves," Mr Trenin says. "Misha is best remembered here for launching an attack on South Ossetia."
In fact, Mr Saakashvili allowed himself to be lured into a trap after weeks of provocations in South Ossetia by launching an ill-advised assault on the Georgian breakaway region, which provided the pretext for Russia's 2008 invasion. Russian media's evocation of his role then may be just another way of Moscow registering chagrin over his Odessa appointment.
But Ukraine's ending of Russian military access to Transnistria - however understandable - does pose a logistical problem for Moscow. And it is a reminder, in the new climate of east-west antagonism, of just how many potential flashpoints lurk in the zone between the two.