Armenia dragged rival Azerbaijan to the UN's top court on Thursday, accusing it of decades of rights abuses including last year's war over a disputed region.
Yerevan is calling on the International Court of Justice (ICJ) to take emergency measures to "protect and preserve Armenia’s rights", the Hague-based tribunal said in a statement.
Azerbaijan said it would "hold Armenia to account" for what it said were rights abuses against its own people, reported Agence France-Presse.
Armenia's case is based on an allegation that Azerbaijan has breached a UN treaty, the International Convention on the Elimination of All Forms of Racial Discrimination (ICERD).
"For decades, Azerbaijan has subjected Armenians to racial discrimination," the filing says, "with Azerbaijan’s President Ilham Aliyev himself leading the way".
"As a result of this state-sponsored policy of Armenian hatred, Armenians have been subjected to systemic discrimination, mass killings, torture and other abuse."
Armenia also says that the alleged violations "once again came to the fore in September 2020, after Azerbaijan’s aggression".
The ICJ was set up after World War II to rule on disputes between United Nations member states. Cases usually take years to reach a conclusion.
Decades of tensions over Azerbaijan's breakaway region of Nagorno-Karabakh erupted into a six-week war last autumn that claimed more than 6,500 lives.
It ended in November with a Russian-brokered ceasefire under which Armenia ceded territories it had controlled for decades.
Nagorno-Karabakh is an ethnic Armenian region of Azerbaijan that broke away from Baku's control in the early 1990s after the collapse of the Soviet Union. Around 30,000 people have died during the conflict.
- 'Grave breaches' -
Azerbaijan said it would launch its own legal proceedings in response to the Armenian move.
"In the coming days, we will hold Armenia to account for breaches" of the discrimination convention, Azerbaijan’s deputy foreign minister Elnur Mammadov said in an English-language tweet.
"Thirty years of human rights abuses against Azerbaijanis during occupation will not be tolerated."
The Azerbaijan foreign ministry said it had been "carefully documenting and compiling evidence of gross human rights abuses" by Armenia for its own legal action.
"This includes Armenia’s targeting of Azerbaijanis for expulsion, torture, murder and serious mistreatment,"
"We will not tolerate these grave breaches of ICERD by Armenia, and will be seeking justice under international law as soon as possible."
Both sides have long traded accusations of rights abuses, including in last year's war.
In February, the foreign ministers of Armenia and Azerbaijan both addressed the United Nations Human Rights Council over their claims that the other side violated international law.
Armenia accused Azerbaijani forces of targeting civilian infrastructure and destroying Armenian cultural and religious heritage.
Azerbaijan, which was backed by Turkey during the conflict, for its part accused Armenian forces of war crimes.
In December, Amnesty International urged Baku and Yerevan to urgently probe "war crimes" committed by both sides during the fighting.
While Armenia has not opened an investigation into its army for war crimes, Azerbaijan has charged two of its soldiers for mutilating bodies of Armenian soldiers.
In the 1990s, Armenian-backed separatists in Nagorno-Karabakh declared independence from Azerbaijan in a war over the mountainous province that left some 10,000 dead.
Armenia's ally Russia refused to intervene militarily in the latest conflict last year, but deployed several thousand peacekeepers to Nagorno-Karabakh after brokering the peace accord in November.