They said Hamas is emerging as the lynchpin of Palestinian terrorist activities against Israel.
While Hamas is maintaining a front of abiding by the cease-fire with Israel in the Gaza Strip, it is providing Qassam rockets to Islamic Jihad militants who are targeting Israeli towns in the south, the security sources said.
Meanwhile, for the first time on Thursday, Hamas extremists openly demonstrated against the leadership of the group.
A group of nearly 200 gunmen from the military wing of Hamas and the Executive Force demonstrated in the Jabaliya refugee camp in the Gaza Strip against the unity government and declared that they will only abide by orders from the former foreign and interior ministers, Mahmoud Al-Zahar and Said Sayam.
Another reason for the mutiny revolves around disputes over the identity of the Palestinian prisoners on a list provided to Israel recently, for a possible exchange for the release of abducted IDF soldier Gilad Shalit.
Some of the demonstrators argued that the list of prisoners was prepared by those prisoners' relatives.
A meeting scheduled Wednesday between Nizar Riyan, a senior figure in the political leadership of Hamas, and members of the "rebels" ended with an exchange of gunfire near Riyan's home.
According to security sources, Hamas has adopted a strategy of duality, which will be maintained under all circumstances, including a situation of a general cease-fire. On the basis of this strategy, a Palestinian organization will continue violent activities against Israel notwithstanding a cease-fire.
This was a similar strategy used by Yasser Arafat, who committed the PLO in agreements to preserve cease-fires, but was always careful to retain his ties with extremist organizations that would continue their terrorist activities against Israel.
In the past, Israeli intelligence provided evidence exposing this strategy.
As such, so long as Hamas continues to cooperate with Islamic Jihad, sources say that the value and reliability of a cease-fire agreement is dubious.
The cooperation between Hamas and Islamic Jihad involves an agreement not only to turn a blind eye to the rocket attacks against Israel, but also to provide the militants with the hardware.
It is believed that Hamas had provided Islamic Jihad militants with Russian-made Grad rockets with a range of 16 kilometers, and which were used to target Ashkelon on June 18, 2006.