The heaviest clashes between Armenia and Azerbaijan since 2016 have reignited concern about stability in the South Caucasus, a corridor for pipelines carrying oil and gas to world markets.

The dispute between the two former Soviet republics, which fought a war in the 1990s, were the latest in a long-running conflict over Nagorno-Karabakh, a region that is inside Azerbaijan but is run by ethnic Armenians.

Nagorno-Karabakh said 16 of its serviceman had been killed and more than 100 wounded after Azerbaijan launched an air and artillery attack early on Sunday.

SUBSCRIBE to our YouTube channel for more videos: http://www.youtube.com/skynews

Follow us on Twitter: https://twitter.com/skynews

Like us on Facebook: https://www.facebook.com/skynews

Follow us on Instagram: https://www.instagram.com/skynews

For more content go to http://news.sky.com and download our apps:

Apple: https://itunes.apple.com/gb/app/sky-news/id316391924?mt=8

Android https://play.google.com/store/apps/details?id=com.bskyb.skynews.android&hl=en_GB

Sky News videos are now available in Spanish here/Los video de Sky News están disponibles en español aquí https://www.youtube.com/channel/UCzG5BnqHO8oNlrPDW9CYJog