Unknown assailants in the Gaza Strip have shot dead a senior Hamas member, officials in Gaza said, blaming Israel for the killing.

Iyad al-Bozum, an interior ministry spokesman in the Hamas-ruled Gaza Strip, said that gunmen opened fire on Mazen Faqha in the Tell al-Hama neighbourhood, adding that an investigation into the incident has been launched.

"Hamas and its military wing hold Israel and its collaborators responsible for this despicable crime... Israel knows that the blood of fighters is not spilled in vain and Hamas will know how to act," the group said in a statement.

Another senior Hamas official, Izzat El-Reshiq, said the killers used silencers on their weapons during the attack.

Police spokesman Ayman al-Batniji said Faqha had "four bullets in his head" and said Israel and its "collaborators" were responsible for the killing. "We know how to respond to this crime," he added.

Faqha, 38, 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.

Shalit was held in the coastal enclave after being seized in a cross-border raid in 2006.

An Israeli military spokeswoman declined to comment on the assissination in the Hamas-run Palestinian coastal enclave, which has been under Israeli blockade since 2006.