At least 170 soldiers have been killed in the deadliest clashes between Armenia and Azerbaijan since a 2020 war.

The fighting, which each side blamed on the other, has threatened to drag Russia, Armenia's ally, and Turkey, Azerbaijan's key backer, into a wider conflict at a time of already high geopolitical tensions.

Here's a look at the ongoing conflict and why it matters.

What are Armenia and Azerbaijan fighting over?

Armenia and Azerbaijan, two former Soviet countries in the south Caucasus, have been fighting for decades over Nagorno-Karabakh, a mountainous enclave internationally recognised as part of Azerbaijan but which until 2020 was populated and fully controlled by ethnic Armenians.

In a six-week war that year, Azerbaijan won significant territorial gains in and around Nagorno-Karabakh.

The fighting was ended by a Russian-brokered ceasefire, but skirmishes have erupted periodically since then despite the presence of Russian peacekeepers.

In the latest flare-up, Yerevan said several Armenian towns were attacked overnight.

Azerbaijan said it was responding to Armenian provocations.

Why has fighting broken out now?

The timing is significant because Russia has in the past been the most influential mediator between Armenia and Azerbaijan.

Although the Kremlin said on Tuesday that President Vladimir Putin was making every effort to curb bloodshed in the south Caucasus, the war in Ukraine has undermined Moscow's status as a peace guarantor in the region.

That may have emboldened Azerbaijan to pursue more claims.

Azerbaijan and Armenia categorically disagree on what a comprehensive peace agreement should look like.

While Baku wants to dissolve Nagorno-Karabakh as a political entity and bar Yerevan from playing a role there, Armenian authorities have pledged to ensure the rights of local Armenians.

What are the risks?

A full-fledged conflict between Armenia and Azerbaijan risks dragging in the big regional powers, Russia and Turkey, and destabilising the south Caucasus, an important corridor for pipelines carrying oil and gas, at a time when the Ukraine war is already disrupting energy supplies.

Moscow has a defence alliance with Armenia and operates a military base there, while Ankara backs its ethnic Turkic kin in Azerbaijan both politically and militarily.

A war between Armenia and Azerbaijan could create a need for more peacekeepers, at a time when Moscow could ill-afford to provide them.

REUTERS