Despite the recent landmark agreement providing for a prisoner exchange between Israel and the Palestinian militant group Hamas, violence continues unabated in the region.

Five Palestinian militants in the southern part of the Gaza Strip were killed by Israeli air strikes early Saturday morning. They were believed to be members of Islamic Jihad and were at a military training facility in Rafah. Ten other people were also reported to have been injured in the attack.

Islamic Jihad -- which is not directly affiliated with Hamas -- said it will take revenge for the killings.

Our response shall be in the depths of the Zionist entity, it said in a statement.

A spokesman for Islamic Jihad also said one of the fatalities was a local field commander, Ahmed Sheikh Khalil.

Today it was a great loss for us in the Islamic Jihad, he said. The size of our retaliation will equal our loss.

The Israeli air force confirmed the attack and defended its move by claiming that the militants were planning to launch rocket missiles into Israel. They also said Islamic Jihad had fired a missile into the city of Ashdod in southern Israel on Wednesday.

Indeed, a few hours after the attack on its people, Islamic Jihad fired a rocket into Israel, which injured one person.

The Israeli military also released a statement saying it had attacked three terrorist sites in the Gaza Strip, as well as an arms factory in the south of the territory. One of those targets reportedly belonged to Hamas.

Israel directly blamed Hamas for the renewed violence.

The Hamas terror organization is solely responsible for any terrorist activity emanating from the Gaza Strip, the Israeli military said.

A spokesman for Hamas, Fawzi Barhoum, replied that Israel is fully responsible for all the results of this dangerous escalation.

The incident threatens to postpone or cancel the planned release of 500 more Palestinian prisoners from Israeli jails. (Israel had previously freed about 500 Palestinian inmates in exchange for the release of Israeli solider Gilad Shalit, who had been held by Hamas for five years.) Some of the freed prisoners also belonged to Islamic Jihad.

Islamic Jihad is believed to be supported by Iran and has been implicated in a number of attacks and suicide bombings against civilians in Israel during the second Palestinian intifada (uprising).