Ukraine on Tuesday accepted the International Criminal Court's jurisdiction to probe war crimes committed since February 2014, including in its war-torn east where thousands have been killed.
The move also opens the door to investigate the downing of Malaysia Airlines flight MH17 in which 298 people -- mainly Dutch -- died in July last year, civil groups said.
"Ukraine accepts the jurisdiction of the court for the purpose of identifying, prosecuting and judging perpetrators and accomplices of acts committed on the territory of Ukraine since February 20 2014," said a letter, signed by Foreign Minister Pavlo Klimkin and accepted by the Hague-based court.
Although Ukraine is not a state party to the court, it can accept the ICC's jurisdiction on a case-by-case basis for crimes committed within a particular time frame.
Ukraine has already given the ICC the green light to probe alleged crimes committed between November 21, 2013 when pro-EU demonstrations erupted in Kiev and February 22 last year, when pro-Moscow president Viktor Yanukovych was ousted.
"What it means is that the prosecutor will now be able to probe crimes after February 22 last year, with an open-ended time frame," ICC spokesman Fadi El Abdallah told AFP.
This includes the conflict in eastern Ukraine, where nearly 8,000 people -- including civilians, soldiers and militia members -- have been killed since mid-April 2014, according to the latest UN figures.
- 'No automatic investigation' -
The ICC's chief prosecutor Fatou Bensouda in April last year opened a preliminary probe into the crimes committed before February 22, 2014.
The ICC however warned on Tuesday "the acceptance of the court's jurisdiction does not automatically trigger an investigation."
"It is for the ICC prosecutor to decide whether or not to request the judges' authorisation to open an investigation," it said in a statement.
Opened in 2003, the ICC is the world's only permanent independent court set up to try the worst crimes like genocide, war crimes and crimes against humanity.
Earlier on Tuesday, the United Nations human rights office (OHCHR) in Geneva said at least 7,962 people in eastern Ukraine had been killed and more than 17,811 wounded since mid-April 2014.
Its report highlighted brutality in the rebel-controlled territories of Donetsk and Luhansk but also drew attention to "a persistent pattern of arbitrary and incommunicado detention" by Ukrainian forces in areas controlled by Kiev.
- 'Clear signal' -
In a message on Twitter, Klimkin said Ukraine would work with the court.
"Ukraine will cooperate with the court to end impunity for international crimes," he wrote.
Rights organisations praised the move to petition the court, saying Ukraine's willingness to expand the acceptance of ICC jurisdiction "is a clear signal of its commitment to accountability for grave crimes and an important step towards ending impunity."
"Numerous war crimes and crimes against humanity have been committed in the eastern Ukraine since February 2014, including violence against civilians and the shooting down of Malaysia Airlines flight MH17," the umbrella Coalition for the ICC said in a statement.
"Ukraine has taken a crucial step towards ending violence and armed conflict in the east of the country," added Roman Romanov, director of the Ukraine-based International Renaissance Foundation.
Kiev in June issued a formal notification saying it was unable to uphold major human rights conventions in pro-Russian separatist-controlled areas, in a de facto acknowledgement that it no longer had sovereignty over all of Ukraine.
Warring sides in Ukraine however have marked a week without heavy fighting, in a tentatively encouraging sign that came after rebels pledged renewed commitment to a peace deal, inked in Minsk in February.
Some analysts have speculated the move has been driven by Russian President Vladimir Putin's need to end Western-imposed sanctions that have battered his country's faltering economy.