Palestinian riot police fired in the air Saturday to keep back dozens of stone-throwing trespassers, and cranes and bulldozers plugged breaches along the porous Gaza-Egypt border, in the first signs of a clampdown after days of chaos.

The fate of the border and a new Israeli demand that the terrorist group Hamas (search) be barred from upcoming Palestinian elections are expected to be raised at an upcoming meeting between Israeli Prime Minister Ariel Sharon (search) and Palestinian leader Mahmoud Abbas (search). A summit is tentatively set for Oct. 2, Palestinian negotiator Saeb Erekat said Saturday.

The border mayhem is emerging as Abbas' most immediate test as he tries to assert control in Gaza after the Israeli withdrawal a week ago. Thousands have crossed between Gaza and Egypt in recent days, virtually without controls, to shop or reunite with relatives after years of separation, but also to smuggle weapons and drugs.

Abbas is faced with a dilemma. He needs to secure freedom of movement for his people ahead of parliament elections in January, and that means keeping the Gaza-Egypt border open. However, the chaos increasingly makes him look weak in the eyes of the world, and will make it tougher to negotiate a future border deal with Israel.

Israeli Foreign Minister Silvan Shalom told Israel Radio that recent events in Gaza "were not encouraging," and that it's unlikely Israel will make more concessions if the Gaza experiment fails.

On Saturday morning, helmeted Palestinian riot police patrolled the border strip, checking documents and bags of Palestinians returning from Egypt. Police also prevented Gazans from entering Egypt, witnesses said.

At one point, dozens of Gazans waiting at the border threw stones at police, who fired in the air for several minutes and threw stones back at the crowd. One man was wounded in the hand by shrapnel, hospital doctors said.

Later in the day, Palestinian bulldozers and cranes began closing holes in the border barriers. A crane piled large cement blocks on top of each other. On the Egyptian side, border guards rolled out barbed wire to keep out trespassers.

Abbas said Friday evening, after a meeting with senior Egyptian officials, that he hoped to restore order along the border in coming days. However, the Palestinians say they can only do so if the border's Rafah crossing — closed by Israel as part of the pullout — is reopened quickly for passenger traffic.

Israel says Rafah needs to remain closed for at least six months, both for a technological update and to test Abbas' ability to control militants in Gaza. In the meantime, traffic from Gaza would be routed through alternate Israeli-controlled crossings. The Palestinians have rejected the proposal.

Erekat, the Palestinian negotiator, said he expects the issue to be raised in the Abbas-Sharon meeting.

In another sign of a clampdown, Palestinian police on Saturday arrested six Palestinians for looting greenhouses in abandoned Jewish settlements. American Jewish donors had bought more than 3,000 greenhouses from Israeli settlers for $14 million and transferred them to the Palestinians to secure thousands of farming jobs. In recent days, officials estimated looters had taken about 30 percent of the greenhouse equipment.

Sharon, meanwhile, demanded that Hamas be excluded from the Palestinian parliament election.

Sharon told The New York Times that if Hamas runs, Israel could make it difficult for Palestinians in Jerusalem and the West Bank to reach polling stations, by not easing travel restrictions on the day of the vote. "I don't think they (Palestinians) can have elections without our help," Sharon told the newspaper.

Hamas is responsible for dozens of deadly attacks on Israelis in the past two decades, and Hamas leaders have said the group will continue to build its private army and carry out attacks in Israeli-controlled areas.

Abbas hopes Hamas, which is expected to make a strong showing in the election, will eventually transform itself into a political party and disband its armed wing.

Palestinian negotiator Saeb Erekat said any Israeli interference would only hurt Abbas and strengthen Hamas.

"I urge the Israelis to stay out of our elections and our internal affairs, and not to put their noses in this," Erekat said. "Our election ... will be a turning point toward political pluralism and toward maintaining law and order."

Mohammed Ghazal, a Hamas leader in the West Bank, accused Israel of acting in an undemocratic fashion.

"Israel claims that it is the democratic state in the region but in fact it fights democracy in Palestine," he said. "If we win the Palestinian election, our top priority will be rebuilding the economic and social and cultural life, rebuilding what Israel has destroyed. We are not thinking of destroying Israel."

Also Saturday, the Palestinian Authority announced it has appointed veteran diplomat Riyad Mansour to head the Palestinian observer mission to the U.N. Mansour will replace Nasser al-Kidwa, the Palestinian foreign minister. Mansour worked as al-Kidwa's deputy at the Palestinian mission to the U.N. for the past 15 years.