Two months ago, a Ukrainian military officer told me he saw an 'incident' with Russia coming – he didn't think it would be this soon

The clashes between Moscow and Kiev in the Azov Sea were not a matter of surprise. Tension has been rising along with likelihood of a front line on water as well as the one on land with the separatist eastern Ukraine. The question now is whether this will be a contained confrontation or pave the way towards wider conflict.

Two months ago I was at an international conference in Kiev, where the US special representative to Ukraine declared that the presence of Russian forces on the Azov Sea was a “provocative aggressive act which was a matter of deep concern”. Washington had just reversed the policy of the Obama administration and started sending Javelin missiles to Ukraine, and Kurt Volker stressed that further supplies of offensive weaponry were being considered.

Later that week, at the port of Odessa – a city that experienced one of the worst acts of violence during the civil war in which 46 people burnt to death – there was unease about what lay ahead. A Ukrainian military officer I met wondered whether he would be able to get back to his home city of Lviv for Christmas or whether he’d find himself on active duty.

The officer was wrong about the timing. The “incident” he thought would take place came earlier than expected. On Sunday three Ukrainian vessels, two gunboats and a tug that sailed out of Odessa were seized by the Russian special forces, who opened fire while boarding, injuring between three to six Ukrainian sailors. Moscow has now stated that it will prosecute 23 people on board the ships – who included Ukrainian intelligence officers – with making an illegal border crossing, dismissing Kiev’s call to treat them as prisoners of war.

The Kremlin claims that the clash on the Azov Sea was an act of deliberate “provocation”, a word much used by both sides in the separatist conflict. Russian state television showed interrogations with three of the sailors in which one of them, who identified himself as Vladimir Lisov, said, “I recognise that the actions of the ships with military hardware of Ukraine’s navy had a provocative character. I was carrying out an order.” It was distasteful footage, with indications that the statement may have been made under duress.

This was the first overt military exchange between the two countries since four years ago when I watched Moscow’s military take over Crimea. I subsequently met Russian soldiers fighting in the Donbas while reporting on the conflict, but was told that they were “volunteers on leave” from their units.

The annexation of Crimea changed the physical dynamics of the Azov Sea and its access route, the Kerch Strait. Under a 2003 agreement, the strait was meant to be shared between Ukraine and Russia, with the two countries flanking its western and eastern shores. With control of Crimea, Moscow now holds both sides. A 12-mile bridge linking Crimea and Russia has now been built, with Vladimir Putin, who had complained about Crimea being “given away to Ukraine like a bag of potatoes” by Nikita Khrushchev, personally driving a truck across it.

Russia quickly enlarged its naval presence in the area after the annexation, and vessels trying to get to Ukrainian ports – from Mariupol in the north to Odessa in the south – found themselves facing time-consuming and commercially damaging delays through inspections. Ukraine claimed that the Kremlin was breaching the 2003 deal and effectively carrying out a blockade; Moscow insisted that the checks were necessary on security grounds.

Inside Ukraine and elsewhere, there are claims that it suited President Petro Poroshenko in Kiev, trailing in the opinion polls in the elections due in four months’ time, to find a threat to national security. Martial law has been declared in border areas for 30 days – the first time since the uprising which overthrew the pro-Moscow government of Viktor Yanukovych in 2014. This, say critics, will affect campaigning for the election.

Russia called a meeting of the United Nations Security Council to address what it called “Ukrainian violations of Russian territorial waters”. The session, however, was quickly turned into a mass criticism of Moscow’s actions in Ukraine by western states.

Ukraine, in turn, requested a meeting with Nato, following which secretary general Jens Stoltenberg wanted to stress that “what you saw was very serious, because you saw actually that Russia used military force in an open way. That is escalating the situation in the region and confirms a pattern of behaviour which we have seen over several years.”

Ukraine, however, is not a Nato member – and it remains to be seen what steps, if any, the alliance will take. There has been talk in the past of exercising “right of navigation” by sending warships through the Azov Sea, but there is unlikely to be appetite for such a high-risk move in the current febrile climate.

Any really strong western response would depend on the US. Donald Trump, asked for his reaction to ship seizures, refused to blame Russia. “Not good, we’re not happy about it at all. We do not like what’s happening either way,” he said. This is a president who has said that his administration may reverse US policy and recognise Crimea as now part of the Russian Federation. It is highly improbable, whatever some people in his administration may want, that he will sanction combative action.

The European Union has called for de-escalation of the situation and Angela Merkel’s office said she reinforced the need for it in a telephone call to Putin. The Russian president will meet fellow world leaders at the G20 summit in Buenos Aires at the end of the week and is likely to face criticism from some of them. But Russia’s control of the Strait of Kerch, Ukraine’s access to the Azov Sea, is unlikely to be loosened.