Yahya Sinwar, considered one of Hamas’s most ruthless leaders, has been elected as the terror group’s leader in the Gaza Strip, a Hamas official confirmed Monday.

Sinwar, 55, generally avoids the limelight, but is seen as an unpredictable hardliner who inspires the loyalty of Hamas’s military wing’s leadership.

He will replace Ismail Haniyeh, who is running for the leadership of Hamas’s political bureau to succeed Khaled Mashaal.

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Sinwar, sentenced to life in 1989 for murdering Palestinian collaborators with Israel, spent 22 years in Israeli prisons before being released in the 2011 prisoner exchange deal for IDF soldier Gilad Shalit.

In September 2015, Sinwar was added to the US terrorism blacklist alongside two other members of Hamas’s military wing, the Izzedine al-Qassam Brigades.

A graduate in Arabic, he was born in the Khan Younis refugee camp in southern Gaza and founded “Majd,” one of Hamas’s intelligence services.

Khalil al-Hayya, a Hamas lawmaker since 2006 and a member of the group’s political bureau, was chosen as Sinwar’s deputy, Arab media reports said.

An online image showed a picture of Hayya, on the left, and Sinwar, on the right.

قناة الجزيرة: حماس تنتخب يحيى السنوار مسؤولا لها بغزة وخليل الحية نائبا له. pic.twitter.com/Ix7ORvrH2L — فلسطين بوست (@plespost) February 13, 2017

Hamas has been conducting secret internal elections since the start of January.

Hamas has four constituencies — activists in Gaza, the West Bank and exile, and members imprisoned by Israel. Each of the four groups chooses local leaders as well as delegates to the group’s Shura Council.

Hamas still needs to elect a new political chief to replace Mashaal, who has announced he’ll step down. The front-runner for that position is believed to be Haniyeh, the former Palestinian prime minister and outgoing Gaza chief, who is currently Mashaal’s deputy. Those elections are expected to conclude in the coming months.

The election of Sinwar as Hamas’s Gaza leader signals the ascendance of the terror group’s military wing, the Qassam Brigades, which now holds more sway in the Strip than the political leadership.

He is considered hawkish even within Hamas, and opposes any compromise in its policies regarding the Palestinian Authority and Israel. Even from prison, he was one of the main opponents of the Shalit exchange deal that saw him freed because he regarded the terms, one Israeli soldier for 1,027 prisoners, as a surrender to Israel’s conditions.

Since his release, he has managed to amass a great deal of political power in Hamas, and was already widely considered the strongest man in Gaza even though he was not the head of Hamas’s military or political wing.

Washington accuses him of continuing to advocate kidnapping of Israeli soldiers as a bargaining chip for Palestinian prisoners.

Hamas currently claims to have four Israelis in captivity in Gaza, though Israel says the two soldiers among them were killed in the 2014 war.

Kobi Michael, an analyst and former head of the Palestinian Desk at Israel’s Ministry for Strategic Affairs, said the appointment would cause alarm among Israeli politicians.

“He represents the most radical and extreme line of Hamas,” he told reporters. “Sinwar believes in armed resistance. He doesn’t believe in any sort of cooperation with Israel.”

Read: Yahya Sinwar can ignite Israel’s south — and may want to

Israel has fought three wars with Hamas since 2008, the last of which in 2014.

The Jewish state maintains a security blockade on Gaza to prevent the terror group, which seized control of the Strip in 2007 from Fatah and is avowedly committed to destroying Israel, from importing weaponry.

Avi Issacharoff and AFP contributed to this report.