Almost five years into a conflict between Russia and Ukraine, tensions have flared again. This time the clash is at sea, where Russian forces fired on Ukrainian warships in the strategic Kerch Strait, capturing three vessels. The incident threatens to disrupt a key shipping chokepoint and reignite the simmering conflict that has claimed more than 10,000 lives and fueled a Cold War-style standoff. It could also derail Ukraine’s efforts to rebuild its economy and hold elections next year.

1. Are Russia and Ukraine at war?

The fear of a full-blown war between Ukraine and Russia has been ever-present since the conflict started in 2014. While a 2015 agreement ushered in a relative lull in the fighting, the Russian attack against Ukrainian warships rekindled old anxieties. Yet, even as Ukraine’s President Petro Poroshenko vowed to punish Russia and discussed the introduction of martial law, he himself made it clear that this doesn’t mean war and promised that Ukraine wouldn’t go on a military offensive.

2. Why is the Kerch Strait a flashpoint?

The Kerch Strait is a narrow waterway linking the Sea of Azov, where Ukraine has several ports, to the Black Sea and on to European and global markets. Russia has built a $3.7-billion, 19-kilometer (12-mile) bridge across as the only direct link between its mainland and Crimea, the peninsula it seized from Ukraine in 2014. Ukraine complained in July, several months after the bridge was opened, that Russia is using the structure to limit maritime activity. It’s become a chokepoint of regional significance in the global food trade since -- a major export channel for grains, oil, minerals and timber.

3. Is this the first conflict in the strait?

The waterway has sparked tensions between Ukraine and Russia well before the recent conflict. In 2003, the countries wrangled about a small island in the strait, situated just on the maritime border between the two post-Soviet nations. Having annexed Crimea, Russia also occupied the whole of the Kerch Strait. On Sept. 23, a small group of Ukrainian military vessels passed under the bridge unhindered. This time, Russia chose to stop the Ukrainian Navy by force.

4. Why the call for martial law and what would that mean?

Based on the draft law lawmakers in Kiev will start discussing the measure at 4 p.m. local time, martial law would last 60 days. Some details of the bill have emerged:

• It would cover the whole country, not just regions in the immediate area

• It would begin Monday and remain until Jan. 25

• Calls for partial military mobilization

• Strengthens border controls and air defense of major government sites, industrial areas and troops

• One clause is marked secret and its details won’t be made public.

Just as importantly, here’s what we know the law wouldn’t involve:

• No immediate mobilization would take place even as the country’s military went to full readiness and reservists were put on alert

• Political freedoms would not be curtailed

• No military offensive will take place and the situation on the front line with the areas held by Russia-backed separatists would not change

• It wouldn’t necessarily mean a delay in next year’s elections

• It probably wouldn’t influence financial side of things, including the aid from IMF.

5. Why is the conflict flaring up now?

Tensions have been building since the bridge was finished in May and Russia tightened control over the waterway. And while the leaders of Russia and Ukraine might look at each other through cross-hairs, they have one thing in common: sagging approval ratings. Putin’s popularity is now the lowest since the widely popular Crimea takeover. Poroshenko is heading into next year’s presidential elections facing a substantially more more popular challenger, former Prime Minister Yulia Tymoshenko. Opposition politicians already accused the Ukrainian president of seeking to impose martial law in a bid to delay next year’s ballot.

Also, the incident comes less than a week before Group of 20 leaders meet for a summit in Buenos Aires. In past years, flare-ups in the Ukrainian conflict have often preceded major rounds of peace negotiations or international summits where Russia participated. While some in the international community have already called for further sanctions against Moscow, many of Putin’s counterparts will head into the meeting with their own domestic difficulties, from Brexit to the U.S. midterm elections.

--With assistance from Daryna Krasnolutska, Volodymyr Verbyany, Marton Eder, Olga Voitova and Áine Quinn.

To contact the reporter on this story: Aliaksandr Kudrytski in Minsk, Belarus at akudrytski@bloomberg.net

To contact the editors responsible for this story: Balazs Penz at bpenz@bloomberg.net, Torrey Clark

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