Israel (search) and the Palestinian Authority on Thursday said they fear Al Qaeda terrorists will infiltrate into Gaza through the open Gaza-Egypt border, where Palestinians and Egyptians have been crossing largely unfettered since Israel withdrew from the area four days ago.

In a deal worked out with Israel, Egypt (search) is supposed to deploy 750 border troops to secure the frontier and prevent weapons smuggling, but neither those troops nor Palestinian policemen have been able to halt the flow of people and arms, including hundreds of assault rifles and pistols.

Israel fears international terrorists will exploit the chaotic border to infiltrate Gaza (search) and Israel.

"We're talking about Iran, we're talking elements in Syria, we're talking about groups like Hezbollah and we're talking also about international terrorist groups like Al Qaeda," said Israeli foreign ministry spokesman Mark Regev. Israel has long accused Iran and Syria of sponsoring militant groups.

Rafiq Husseini, the top aide to Palestinian leader Mahmoud Abbas, said, "we are even more worried than Israel about Al Qaeda coming here because Al Qaeda will harm us more than Israel." Such a presence, he said, would hurt prospects for peace and renewed negotiations with Israel.

"The Palestinian Authority security apparatus will arrest any suspected Al Qaeda members or other terrorist groups if they infiltrate Gaza," he said.

Al Qaeda has been active in northern Egypt but there has been no indication they've infiltrated Gaza, which until this week has been tightly sealed.

Its operatives are prime suspects in a triple bombing that killed at least 64 people in July at Egypt's popular Red Sea resort of Sharm el-Sheik on the southern tip of the Sinai. That attack came 10 months after bombings at two other Sinai resorts near the Israeli border, Taba and Ras Shitan, killed more than 30 people.

Senior Israeli military officials said they feared Al Qaeda operatives could enter Gaza from Sinai and connect with the local Hamas militant group to share expertise and provide weapons.

Regev and other officials said Israel fears that militants will leave Gaza and enter Israel through the Egypt-Israeli border in the Sinai Desert, an unfenced frontier. The Egypt-Israel border has long been a favorite crossing point for drug runners, illegal workers and prostitutes.

Israel's border patrol on Thursday arrested 20 Gazans trying to get into Israel through Sinai, according to Israeli media reports.

One Palestinian official rejected the Israeli accusations of terrorist infiltration, calling them "ridiculous" and "a complete lie."

"Israel withdrew from the border without coordination and Israel shoulders the responsibility for the actions that took place on the border," said Palestinian Interior Ministry official Tawfiq Abu Khoussa. He said Palestinian and Egyptian forces will soon restore order at the frontier.

He added Gaza's people would not tolerate an Al Qaeda presence in their midst.

"The Palestinian Authority doesn't welcome them and the Islamic movements, like Hamas and Islamic Jihad, have condemned their attacks," Abu Khoussa said.

There were some signs Thursday that security forces were beginning to stem the free flow of people across the border, with Egyptian troops allowing Palestinians to re-enter Gaza but often preventing them from crossing into Egypt. At one point, Palestinian police fired into the air to prevent people from crossing into Egypt, the Haaretz daily reported.

However, in other places Palestinian police and Egyptian troops stood by idly as people crossed over.

Men with one-liter barrels climbed on ladders over a border fence to buy cheap gasoline and diesel fuel in Egypt in full view of two Egyptian policemen, who did nothing.

In another development Thursday, the Israeli Supreme Court on Thursday said that the world court's ruling on Israel's West Bank security barrier was flawed because the international body did not sufficiently consider Israel's security needs.

In July 2004, the International Court of Justice in The Hague, Netherlands ruled that the barrier violates Palestinian rights and should be torn down.

The barrier is meant to prevent Palestinian militants from attacking Israel, but the nine-judge Israeli panel said the world court only considered "the injury to the rights of the Palestinian residents" in its ruling.