Armenia and Azerbaijan, two former Soviet republics, have gone to war twice over the mountainous region of Nagorno-Karabakh in the past century.
Here is a timeline of the troubles:
1923: autonomous Soviet region
The Armenian-majority territory of Nagorno-Karabakh, which is recognised by the international community as part of Muslim-majority Azerbaijan, has changed hands multiple times over the course of history.
In 1813, it became part of the Russian empire and in 1923 was granted the status of autonomous region within the Soviet republic of Azerbaijan.
When the Soviet Union began to crumble in the late 1980s ethnic Armenians in Karabakh began pushing for their region to be ruled by Armenia, a demand rejected by both Azerbaijan and Moscow.
1992: First War
In 1991, after Armenia and Azerbaijan broke away from the Soviet Union, Karabakh's population voted overwhelmingly for independence.
Azerbaijan rejected the poll, which was not recognised by the international community, and the two sides went to war.
Karabakh's Armenians emerged victorious in the 1992-1993 conflict.
They took control of the region as well as a chunk of surrounding Azerbaijani territory connecting it to Armenia.
The war left about 30,000 people dead and forced hundreds of thousands more from their homes.
Ethnic Azeris fled Karabakh and Armenia while ethnic Armenians fled Azerbaijan.
1994: Ceasefire
A ceasefire brokered by Moscow in 1994 left Karabakh and the surrounding territory in Armenian hands.
But deadly clashes continued regularly along the frontier between Karabakh and Azerbaijan.
2020: second war
In a six-week war in 2020, Turkey-backed Azerbaijan won back much of the territory it previously lost.
About 6,500 troops died in the fighting, with the Armenians taking the heaviest losses.
It ended with a Russian-brokered ceasefire.
Under the deal, Armenia ceded large chunks of territory it had controlled for decades.
Moscow deployed some 2,000 Russian peacekeepers to oversee the truce.
Armenians saw the agreement as a humiliation and stormed the main government building in the Armenian capital Yerevan in protest.
2022: Blockade
In September 2022, fighting broke out again with both sides accusing the other of provoking week-long clashes in which more than 210 people died.
In December, Armenia accused Azerbaijan of fuelling a humanitarian crisis after Baku blocked the sole road linking Armenia to Karabakh for cargo deliveries, causing food shortages.
2023: New Azeri Offensive
On September 19, Azerbaijan launched what it calls "anti-terrorist measures" against Armenian separatists in Karabakh, accusing them of deadly mine attacks.
Blasts were heard in Karabakh's main town of Stepanakert.
The separatists said the offensive has so far killed five people and injured 80 others.
Azerbaijan is demanding the total withdrawal of Armenian forces from Karabakh as a precondition for peace.
