The gunmen who assassinated senior Hamas militant Mazen Fuqaha in Gaza City on Friday arrived by sea, unconfirmed reports from the coastal enclave said on Sunday.

Hamas, who has blamed Israel in the assassination and vowed revenge, is being careful not to reveal any details about its investigation into the assassination, one of its senior military commanders said.

Unconfirmed reports said that the assassins carefully collected any evidence of the killing, such as bullet cartridges, that could indicate their identities before immediately fleeing the scene.

Media outlets affiliated with Hamas played up the heavy Israeli press coverage of the assassination, citing this as evidence that Israel was behind the killing.

Fuqaha was sentenced to life in prison and an additional 50 years for planning a suicide bombing on a bus in northern Israel in 2002, where nine Israelis were killed. But in 2011, Fuqaha was released as part of a prisoner exchange deal to free Israeli soldier Gilad Shalit.

Fuqaha, originally from the village of Tubas in the northern West Bank, was exiled at Israel’s demand to Gaza. He was considered a senior member of Hamas’ West Bank command, which gave orders and funds to West bank cells.

The Gaza prosecution accused Israel's espionage agency on Saturday of assassinating Fuqaha, saying the murder "clearly bears Mossad's fingerprints."

Hamas' deputy leader in Gaza said "the released prisoner Fuqaha didn't have enemies, and Israel is the only beneficiary in his assassination. The Al-Qassam Brigades could respond accordingly, and Israel will bear the responsibility."

The Al-Qassam Brigades, Hamas' military wing, released a statement vowing to "respond to the assassination in a manner that befits his position."

Hamas has since closed its side of the Erez crossing between the Gaza Strip and Israel and increased patrols along both the border fence with Israel and the coast.

Fuqaha was a prominent member of Hamas’ military wing in the northern West Bank, which took part of suicide attacks in which hundreds of Israelis were killed during the second intifada, between 2000-2005.