Saleh al-Arouri, the deputy chairman of Hamas' political bureau and the commander of the group's military wing in the occupied West Bank, was killed in a drone attack in a Beirut suburb on Tuesday, Hamas has confirmed.

The big picture: Israel hasn't claimed responsibility for the attack, but one Israeli and two U.S. officials told Axios that Israel was behind the strike. The attack is a serious blow to Hamas and could push the Lebanese Hezbollah militant group to escalate its attacks against Israel.

• The Israeli Prime Minister's Office declined to comment.
• Hezbollah leader Hassan Nasrallah publicly warned Israel several weeks ago against trying to kill Hamas leaders in Beirut. He threatened a strong response if that happened.

Driving the news: Al-Arouri, two Hamas commanders and four other members of the group were killed in the attack on a Hamas office in Beirut, the group said on its Telegram channel. The strike took place near Hezbollah's headquarters in the Beirut suburb of Dahiyeh.

• Hamas said al-Arouri was "one of the architects" of the Oct. 7 terrorist attack against Israel. He is the most senior Hamas leader killed since the war in Gaza began.
• Prime Minister Benjamin Netanyahu said several weeks ago that he ordered Israel's Mossad spy agency to go after Hamas leaders around the world.
• A senior Israeli official told Axios Israel is preparing for a significant retaliation from Hezbollah, which could include the group launching long-range missiles toward targets in Israel.

What they're saying: Hamas leader Ismail Haniyeh called Tuesday's attack a "blatant crime that demonstrates, once again, the brutality that is carried out by the occupation against our people."

• "All these assassinations and attacks will make us stronger and more determined than ever. this is the history of the resistance and our movement. We always become stronger and more determined," Haniyeh said in a televised address.
• He also said the attack was a "violation of Lebanese sovereignty." The "occupation is responsible for any repercussions."

Two U.S. officials told Axios Israel was behind Tuesday's strike but stressed it didn't notify the Biden administration in advance of the attack.

• A senior Israeli official confirmed Israel didn't give the U.S. a heads up but said it notified the Biden administration "as the operation was happening."

Lebanese acting Prime Minister Najib Mikati condemned the attack and called it "an Israeli crime" aimed at drawing Lebanon into the war in Gaza.

• Mikati called on the international community to press Israel to stop its attacks.

Context: Al-Arouri, who is also under U.S. sanctions, was one of the most wanted people by the Israeli intelligence services.

• Israeli officials say he was responsible for the growing number of attacks against Israeli civilians in the West Bank in the last year.

This is a developing story. Please check back for updates.