The International Criminal Court's chief prosecutor said on Friday she would launch a full investigation into alleged war crimes in the Palestinian Territories as soon as the court's jurisdiction had been established.
The announcement opens the possibility of charges being filed against Israelis or Palestinians.
The Palestinians welcomed the decision but Israeli Prime Minister Benjamin Netanyahu, whose country captured the West Bank and Gaza Strip in a 1967 war, said the ICC had no jurisdiction to investigate the Palestinian Territories.
The ICC's chief prosecutor, Fatou Bensouda, said a preliminary examination into alleged war crimes, opened in 2015, had provided enough information to meet all criteria for opening an investigation.
"I am satisfied that ... war crimes have been or are being committed in the West Bank, including East Jerusalem, and the Gaza Strip," Bensouda said in a statement.
She said she had filed a request with judges for a jurisdictional ruling because of the contested legal status of the Palestinian territories.
"Specifically, I have sought confirmation that the 'territory' over which the court may exercise its jurisdiction, and which I may subject to investigation, comprises the West Bank, including East Jerusalem, and Gaza," Bensouda said.
Determining where she can investigate should be resolved before she starts an investigation "and not settled only later by judges after my investigations are completed," she said.
It is not clear when a decision would be made but Bensouda said she had asked the court to "rule expeditiously" and to allow potential victims to participate in proceedings.
"Palestine welcomes this step as a long overdue step to move the process forward towards an investigation, after nearly five long and difficult years of preliminary examination," the Palestinian Authority, a limited self-rule body in the Israeli-occupied West Bank, said in a statement.
Palestinian Foreign Minister Riyad al-Maliki said the ICC decision was "a dark day in the history of Israel".
Netanyahu said the ICC had no jurisdiction in the case.
"The ICC only has jurisdiction over petitions submitted by sovereign states. But there has never been a Palestinian state," he said in a statement.
U.S. Secretary of State Mike Pompeo said in a statement the United States did not believe Palestinians qualified as a sovereign state and added: "We firmly oppose this and any other action that seeks to target Israel unfairly."
The ICC has the authority to hear cases of war crimes, genocide and crimes against humanity committed on the territory of the 123 countries that have signed up to it. Israel has not joined the court but the Palestinian Authority has done so.
The ICC prosecutors said in December that a preliminary investigation on the West Bank had focused on "reported settlement-related activities engaged in by Israeli authorities".
The Palestinians and many countries consider the settlements to be illegal under the Geneva Conventions that bar settling on land captured in war. Israel disputes this, citing security needs and biblical, historical and political connections to the land.
The prosecutor's office has also looked into allegations of Israeli violations in Gaza and that Palestinian security services in the West Bank have committed torture and that Palestinian authorities paid families of Palestinians involved in attacks on Israelis.