The chief of Israel's Shin Bet security service says an agreement to exchange more than 1,000 Palestinian prisoners for captured Israeli soldier Gilad Shalit is the best deal possible.

In a Wednesday news conference, Yoram Cohen said Israel could not guarantee that the Palestinians to be freed will not launch any terror attacks. But, he said if Israel had a better option, it would have chosen it.

On Tuesday, Israel and the Palestinian militant group Hamas announced the deal to free Shalit, who has been held in the Gaza Strip for more than five years. Syria-based Hamas leader Khaled Meshaal said Israel will, in return, free 1,027 Palestinians.

Israel's Cohen says Shalit and about 450 of the Palestinian prisoners will be released within the next week. Officials say the remaining Palestinians are expected to be freed within about two months.

Palestinian militants captured Shalit in a cross-border raid in June 2006 and took him back to Gaza. His prolonged incarceration became another sticking point in the Israeli-Palestinian conflict.

Meanwhile, the Shin Bet chief has denied rumors that Israel's most prominent Palestinian prisoner, Marwan Barghouti, will be included in the release.

Barghouti, arrested in 2002, is serving multiple life terms for his role in deadly attacks against Israelis. Because of his status among Palestinians, he is considered a possible successor to Palestinian President Mahmoud Abbas.

After Israeli Prime Minister Benjamin Netanyahu announced the prisoner swap deal on Tuesday, Shalit's supporters gathered around the tent that his parents have set up outside the prime minister's residence to push for his return.

Shalit's mother said the family's joy is indescribable, but that they will restrain their emotions until he is released.