EXPLAINER-Troubled waters: what's behind the Russia, Ukraine naval standoff?
Kiev accuses Moscow of trying to impose a de facto economic blockade on its ports in the Azov Sea to weaken it as part of a "hybrid war" against Ukraine, and has called for further Western sanctions against Moscow.
The countries have been at loggerheads since Russia seized Crimea from Ukraine in 2014 and backed an insurgency in the eastern Donbass region that has killed more than 10,000 people despite a notional ceasefire.
WHAT'S THE HISTORY OF THE DISPUTE?
Squabbles over control of the Azov Sea and the Kerch Strait, which connects to the Black Sea to the south, are nothing new. Tensions flared in 2003 during Vladimir Putin's first term as Russian president.
These were calmed with a 2003 bilateral treaty stipulating that both countries could use the Kerch Strait and Azov Sea freely for commercial shipping and must notify each other while sending military vessels.
WHAT HAS HAPPENED THIS YEAR?
Tensions have increased in the area this year, with Ukraine accusing Russia of persistently detaining ships sailing to and from its ports on the Azov Sea, especially Mariupol and Berdyansk, with a view to disrupting trade.
Mariupol, which was briefly seized by pro-Russian separatists in 2014 before being recaptured by Ukrainian troops and volunteers, is a hub for exporting steel and grain and importing coal.
Ukraine says trade to the ports has been cut by 30 percent since Russia began hassling its ships. Exports from Mariupol have fallen 6 percent and imports by nearly 9 percent this year, while exports from Berdyansk fell by 12.3 percent, data shows.
The bridge is too low for certain vessels to pass through, further hampering trade, Kiev says.
Ukraine says it has now deployed more air, land, sea and artillery forces to the area and plans to build a military base on the Azov Sea.
WHAT HAPPENED ON SUNDAY?
Russia seized three Ukrainian vessels after opening fire on them, wounding several sailors. Russia's FSB security service said the ships - two small Ukrainian amoured artillery vessels and a tug boat - had illegally entered its territorial waters.
Russia accused the ships of manoeuvring dangerously and ignoring its instructions with the aim of stirring up tensions. Ukraine said it had notified Russian authorities in advance of the three ships' movements - in line with the 2003 accord - and denied they had done anything wrong.
Traffic through the Strait resumed on Monday.
WHAT HAPPENS NOW?
Ukraine has put its forces on full combat alert and President Petro Poroshenko has asked parliament to back his decision to impose martial law.
At Kiev's urging, its Western allies could push for more sanctions on Russia, a prospect which pushed the rouble lower on Monday.
The United Nations Security Council will discuss the crisis on Monday at the request of Russia and Ukraine.
Russian politicians have accused Poroshenko of deliberately instigating the standoff to boost his flagging popularity ahead of elections in March. Some Ukrainian opposition politicians have speculated that he is using the introduction of martial law as an excuse to postpone the elections.
(Reporting by Matthias Williams and Natalia Zinets Editing by Gareth Jones)
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)