By Noah Browning

RAMALLAH West Bank (Reuters) - A top Hamas official said members of his militant group kidnapped three Israeli teenagers whose deaths in June provoked a spiral of violence that led to the war in Gaza, the first acknowledgement of the movement's involvement.

Hamas, which controls Gaza, has up to now refused to confirm or deny Israeli accusations that it masterminded the abduction and killing of the three young men, one of them a joint U.S.-Israeli citizen, in Hebron.

"There was much speculation about this operation, some said it was a conspiracy," Saleh al-Arouri told delegates at the International Union of Islamic Scholars in Istanbul on Wednesday, according to a recording of the meeting posted online by organizers.

"The popular will was exercised throughout our occupied land, and culminated in the heroic operation by the Qassam Brigades in imprisoning the three settlers in Hebron," he said, referring to Hamas's armed wing.

"This was an operation from your brothers in Qassam undertaken to aid their brothers on hunger strike in (Israeli) prisons," he added.

Jewish seminary students Eyal Yifrach, 19, and Gilad Shaer and Naftali Fraenkel, both 16, were abducted while hitchhiking in the Israeli occupied West Bank on June 12 and killed.

Israel promptly accused Hamas, which is based in Gaza but has a presence in the West Bank, of masterminding the attack and began a crackdown on the group in which over a thousand Palestinians were arrested.

Tensions already ran deep in the West Bank after weeks of a mass hunger strike by Palestinian prisoners in Israeli jails.

Hamas leader Khaled Meshaal, who is in exile in Qatar, denied knowledge of the abduction but praised its perpetrators.

Nearly three weeks after the kidnappings, 16-year-old Mohammed Abu Khudair, a Palestinian living in East Jerusalem, was abducted, beaten and burned to death by, prosecutors said, a group of Jewish extremists.

Protests broke out in Abu Khudair's neighborhood and Hamas responded by firing rockets at Israel from Gaza.

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That escalated into a full-scale war with Israel in which more than 2,000 Palestinians, most of them civilians, have been killed, as well as 64 Israeli soldiers and three civilians in Israel.

Two Palestinian suspects Israel has named as the kidnappers of the three seminary students remain at large.

Israel said a third suspect arrested by its security forces admitted under interrogation to organizing the kidnapping with funds from Hamas in Gaza.

(Writing by Noah Browning; Editing by Luke Baker and Andrew Heavens)