Hamas says it has arrested the killer of senior commander Mazen Faqha, who was shot dead in March, and said the suspect had carried out the assassination on Israel's orders.

Faqha, 38, was fatally shot in the head and chest at the entrance of his Gaza City home on March 24.

"All the evidence we have ... indicates the perpetrator committed this crime based on orders from the Israeli occupation," Ismail Haniya, the leader of Hamas' political wing, told reporters on Thursday, without identifying the suspect.

"He has confessed to the crime," he added, speaking outside Faqha's house in a press conference attended by the commander's widow.

Haniya, who was elected as Hamas's new political chief last week, said more details would be released in coming days, and he expected the suspect to be executed.

Hamas has controlled the Gaza Strip since 2007.

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Faqha was a senior Hamas official in the Israeli-occupied West Bank when he was jailed by Israel in 2003 for planning attacks against Israelis.

He was sentenced to nine life terms but was released into the Gaza Strip as one of more than 1,000 Palestinian prisoners that Israel let go in exchange for soldier Gilad Shalit.

Hamas has previously said Faqha was shot by a gun fitted with a silencer and accused Israel and its "collaborators" for his death.

Israel has not commented on the killing.

"Over the course of 47 days, the security apparatuses worked hard to uncover the threads of Mazen Faqha's assassination crime, until the killer and those who helped him were reached," Iyad al-Bozum, spokesman for Gaza's interior ministry, said in a Facebook post on Thursday.

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A Hamas source said on condition of anonymity that the suspect had "participated in the morning in a reconstruction of the crime", after numerous security forces were seen in front of Faqha's home earlier in the day, according to the AFP news agency.

The Gaza Strip has been under an Israeli blockade for a decade, while Egypt's crossing with the enclave has remained largely closed in recent years.