The mother of Mazen Fuqaha holds his picture in her house in the West Bank town of Tubas. (Abed Omar Qusini/Reuters)

Hamas closed its only civilian border crossing with Israel on Sunday, and Israeli troops were on high alert as tensions between the two enemies continued to rise two days after a senior Hamas operative was mysteriously shot at point-blank range in the garage of his home.

Hamas has accused Israel of being behind the killing of Mazen Fuqaha, 38, a senior commander in the militant Islamist movement’s military wing. He spent nine years in an Israeli prison for his part in planning suicide bombings that killed dozens of Israeli civilians during the second intifada, or uprising, in the early 2000s.

Fuqaha was one of more than 1,000 Palestinian prisoners released in 2011 in exchange for Israeli soldier Gilad Shalit. Upon his release, Fuqaha was barred from returning to his childhood village in the West Bank and expelled to the Gaza Strip. From there, he managed Hamas’s military operations in the West Bank.

His death has brought tensions between Israel and Hamas to their highest level since 2014, when the two sides fought a 50-day war that killed about 74 Israelis and more than 2,100 Palestinians.

[WorldViews: Here’s what really happened in the Gaza war (according to the Israelis)]

This is the first time Hamas has closed the Erez crossing, a checkpoint most frequently used by Gazans seeking health care in Israel and the West Bank. Erez is also used by aid workers and foreign journalists seeking to enter Gaza. Gaza also has a crossing into Egypt, but that is almost permanently closed.

Hamas, which Israel and the United States consider a terrorist organization, set up checkpoints across Gaza in pursuit of those who might have been involved in Fuqaha’s killing.

“We say it clearly that the crime was planned and conducted by the Zionist enemy. And the enemy will be responsible for the crime consequences,” Hamas’s military wing, the Izzedine al-Qassam Brigades, said in a statement.

Israel has not commented on Fuqaha’s death.

Israel has carried out assassinations of Hamas leaders in the Gaza Strip in the past, but the attacks were launched from the air. Such an up-close killing — Gaza’s Health Ministry said Fuqaha was shot at close range with a silencer-fitted pistol — would be almost impossible for Israel to achieve without having people on the inside. Such an attack has not occurred in the coastal enclave since Israel withdrew from the territory in 2005.

Fuqaha’s wife, Nahed Asida, said in an interview with Al Jazeera that the family had just returned from a day out. Her husband went to park the car in their basement garage, she said, and when he did not return for more than half an hour, she thought he had gone to see neighbors. She learned of her husband’s death only when a friend came to tell her.

“I couldn’t believe it at all. It was a shock,” she said. “He received death threats all the time since his release in 2011, but he never paid any attention to it.”

No one has asserted responsibility for the attack, but Israeli media reported Sunday that it was similar in style to the killing of Hamas drone engineer Mohammed al-Zawari on Dec. 15, outside his house in Tunisia. That operation was attributed to the Mossad, the Israeli intelligence agency.

Additionally, Fuqaha’s father told Palestinian media that officers from Shin Bet, Israel’s security agency, had visited him several times, threatening that if his son did not halt attacks on Israel, they would get hold of him. During one such visit, the elder Fuqaha said, he put the agents on the phone with his son.

“He was listed by the Israeli security bodies, and his name was mentioned many times before, but what is surprising is the way the assassination was conducted. It is the first time that Israel has operated in such a way in the Gaza Strip,” said Ibrahim Madhoun, a columnist at the Hamas-affiliated newspaper al-Resalah.

Until now, Israel has used missiles and jets to kill Hamas leaders, he said.

Madhoun said that what might have raised Hamas’s suspicions that Israel was behind the attack is that Fuqaha is not well known in Gaza but is responsible for Hamas’s activities in the West Bank. That would make him a target for Israel.

Israel is bracing for a reprisal. Troops and communities in southern Israel were put on alert throughout the weekend.

Amos Yadlin, former director of military intelligence, said in a public forum Saturday that Fuqaha’s killing could quickly spiral into renewed clashes between Israel and Hamas.

“Hamas could decide that Fuqaha was assassinated by Israel and retaliate, and then we will retaliate to the retaliation, and we could be in another clash very quickly,” he said.

Balousha reported from Gaza City.

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