MOSCOW/KYIV (Reuters) – A Russian troop build-up near Ukraine has led to fears that a war could break out between the former Soviet neighbors. Here are some potential flashpoints.

SEA OF AZOV

Confrontation has periodically flared up in the Sea of Azov, flanked by the Ukrainian and Russian coastlines, since Moscow’s annexation of Crimea in 2014. The sea flows into the Black Sea via the Kerch Strait that Russia now de facto controls. The waters contain two large Ukrainian ports – Mariupol and Berdyansk, where Kyiv is building a naval base. Kyiv says Moscow seeks de facto control of the entire sea and impedes shipping.

Last week Russia accused Ukraine of a dangerous provocation after a Ukrainian naval boat sailed towards the Kerch Strait and did not react to a Russian request to change course. Ukraine said the vessel was an unarmed search and rescue ship and called the complaints disinformation. In 2018, Russia seized two small Ukrainian gunboats and one tugboat and their combined crew of 24 off Crimea. It accused them of illegally entering Russian waters as they headed from the Black Sea via the Kerch Strait.

CRIMEA

Russia has heavily reinforced Crimea with troops and military hardware since the annexation. Ukrainian President Volodymyr Zelenskiy has said he will do all he can to return the peninsula. The Kremlin says it views his comments as a direct threat. Most of the world recognizes Crimea and its surrounding waters as Ukrainian. This summer a British warship exercised what London said were internationally recognized freedom of navigation rules in Ukrainian territorial waters near Crimea. Moscow said the ship crossed into Russian waters and that it fired warning shots and dropped bombs in the path of the vessel.

NORTH CRIMEAN CANAL

The Soviet-era canal that runs for more than 400 km (250 miles) was built in 1961-71 to channel water from the Dnieper river in Ukraine to arid areas of Ukraine’s Kherson region and Crimea. Ukrainian military analysts have said it could be used as a pretext for a Russian military offensive in southern Ukraine.

Following the annexation of Crimea, Ukraine cut off fresh water supply along the canal that had supplied 85% of the peninsula’s needs. Moscow appealed this year to the European Court of Human Rights in part over what it said was Ukraine’s blocking of water supplies. The complaint was dismissed. In July this year, Ukraine’s parliament adopted legislation banning water supplies to “occupied” territories. Kyiv says it cannot supply water because most of it would be used by the Russian army.

Ukraine’s defense minister has said Kyiv would be prepared to supply water to the population in the form of humanitarian aid delivered by the Red Cross if needed, but not via the canal.

DONBASS

Ukraine says some 14,000 people have been killed in fighting between government forces and Russia-backed rebels in eastern Ukraine since 2014. As the West has raised fears over a Russian troop buildup, Moscow has accused Ukraine of building up its own troops and compared the tensions to the run-up to a 2008 war in which Russian forces crushed those of neighboring Georgia.

BELARUS-UKRAINE BORDER

Ties between Ukraine and Belarus have worsened since last year, when Moscow helped Belarusian leader Alexander Lukashenko weather mass street protests and Lukashenko in turn became more vocal in his support for Moscow against Ukraine. He has since said Crimea is legally Russian territory, a U-turn on his previous stance.

Last month, Ukraine said it should set aside money to build a more than 2,500 km fence on its borders with Belarus. Minsk has since accused a Ukrainian Mi-8 military helicopter of flouting its border during maneuvers and flying 1 km (0.6 miles) into its territory. Belarus has announced plans to hold joint military exercises with Russia on the Ukrainian border.

(Reporting by Tom Balmforth and Natalia Zinets; editing by Mark Trevelyan and Angus MacSwan)