EXPLAINER: What's behind Russia-Ukraine tensions?

MOSCOW (AP) — Ukrainian and Western officials are worried that a Russian military buildup near Ukraine could signal plans by Moscow to invade its ex-Soviet neighbor.

The Kremlin insists it has no such intention and has accused Ukraine and its Western backers of making the claims to cover up their own allegedly aggressive designs.

It’s unclear whether the Russian troop concentration heralds an imminent attack. Russian President Vladimir Putin has pushed for Western guarantees precluding NATO's expansion to Ukraine, and the buildup could reflect an attempt to back up the message.

Here is a look at the current tensions:

WHAT ARE THE ROOTS OF THE RUSSIA-UKRAINE STANDOFF?

Ukraine, which was part of the Russian empire for centuries before becoming a Soviet republic, won independence as the USSR broke up in 1991. The country has moved to shed its Russian imperial legacy and forge increasingly close ties with the West.

A decision by Kremlin-leaning Ukrainian President Viktor Yanukovych to reject an association agreement with the European Union in favor of closer ties with Moscow sparked mass protests that led to his ouster in 2014. Russia responded by annexing Ukraine’s Crimean Peninsula and throwing its weight behind a separatist insurgency that broke out in Ukraine's east.

Ukraine and the West accused Russia of sending its troops and weapons to back the rebels. Moscow denied that, charging that Russians who joined the separatists were volunteers.

More than 14,000 people have died in the fighting that devastated Ukraine’s eastern industrial heartland known as Donbas.

A 2015 peace agreement brokered by France and Germany helped end large-scale battles, but efforts to reach a political settlement have failed, and sporadic skirmishes have continued along the tense line of...