The armed branches of Hamas and Palestinian Islamic Jihad in Gaza have formally joined forces to carry out attacks against Israel, the movements’ military spokesmen announced.

Abu-Ubaida, a spokesman for Hamas’ Al-Aqsa Martyr’s Brigade, told Qatari news channel Al-Jazeera on Tuesday that the need to fight Israeli occupation and resist its “divide and conquer” policy brought his movement strategically closer to Islamic Jihad.

Abu-Ahmad, a spokesman for Islamic Jihad’s Al-Quds Brigades, told Al-Jazeera that the two movements have been consulting for months. He said that the new coordination was meant both as a message of unity to Palestinians and as a deterrent to Israel.

The movements claimed joint responsibility for at least 50 mortar shells fired into southern Israel Monday morning. Israel retaliated by targeting Hamas outposts in Gaza.

The Monday attacks — which have been followed by several more instances of rocket fire — marked the first time since June that Hamas had claimed responsibility for firing into Israel. In the past, Hamas has tried at times to dissuade the Islamic Jihad — considered politically less pragmatic — from firing at Israel, fearing Israeli retaliation.

The new-found unity between Gaza’s two main “resistance” movements may be the tip of a larger movement in the Gaza Strip. Abu-Ataya, the spokesman of a third armed faction in Gaza — the Salah A-Din Brigades — suggested Wednesday establishing a joint command center with Hamas and Islamic Jihad to coordinate military retaliation to the “crimes of the occupation.”

Hamas took violent control of the Gaza Strip from Mahmoud Abbas’s Palestinian Authority in 2007. Publicly committed to the destruction of Israel, it has fired rockets into southern Israel for years — before and after Israel’s removal of the settlement enterprise from the Strip in 2005 — gradually expanding its range. Israel has said it holds Hamas responsible for all attacks from Gaza, whether claimed by Hamas or not.