Egyptian riot police and armored vehicles blocked Gaza cars from leaving the Egyptian border town of Rafah, a day after Hamas militants using bulldozers had widened a border breach to make it easier for vehicles to cross.

Armored vehicles blocked the main street of Rafah causing a snarled traffic jam of honking cars filled with Gazans shopping for fuel, food and consumer products, after initially trying to reseal the breached border.

Dozens of riot police had formed human chains to block the two passages cut through the breached border before once again giving up and allowing the cars to cross into the Egyptian side of the divided town. Authorities were making renewed efforts, however, to keep them out of the rest of the country.

The deployment marked the second attempt by Egypt in two days to regain control over the border, which was breached Wednesday when Hamas militants blew down the border wall, allowing hundreds of thousands of Palestinians to flood into Egypt.

Israel, meanwhile, expressed growing concern about the possible influx of Palestinian militants into areas of Egypt that border Israel. The Israeli military announced Saturday that its troops were on heightened alert along the border with Egypt, and that an Israeli road and tourism sites in the area are temporarily closed.

The border breach was engineered by Gaza's Islamic militant Hamas rulers, in an attempt to pressure Egypt to negotiate new border arrangements. Both Israel and Egypt have kept Gaza largely sealed in the past two years, especially since the violent Hamas takeover of the territory in June.

Early Saturday, hundreds of Gaza cars crossed into Egypt.

Palestinians and Egyptians could be seen bypassing the checkpoints around Rafah, however, via dirt roads. In the coastal town of El Arish, about 35 kilometers (20 miles) west Gaza, the roadblocks were tighter and police were witnessed telling shopkeepers to close their stores.

Hundreds of cars with Gaza license plates were seen in El Arish on Saturday, many lining up at gas stations. An elderly Gaza man, Saleh Abu Ghosheh, stood in one of the lines, hoping that a gasoline tanker would eventually arrive to refill the station.

Abu Ghosheh said he was worried the tanker would not show, and that he would have wasted precious fuel getting to El Arish. Still, he said, the trip was not in vain. "It's worth it, at least I bought a goat, dairy products and some items for my children," he said.

The traffic flowed in both directions. Many Egyptian cars were seen in Gaza, including a truck carrying $65,000 worth of cheese, candy bars and cleaning supplies for a Gaza City supermarket.

However, by midmorning, Egyptian riot police and armored vehicles deployed to stop the flow of cars. Egyptian security forces also asked shopkeepers in El Arish to close, apparently to discourage Gazans from driving there. Pedestrians were still able to cross the border.

Egypt faces a dilemma over how to handle the border crisis. If it acts forcefully against the Gazans, it could anger its own people, who are sympathetic to the Palestinians' plight. But if it does nothing, it risks infiltration by Islamic militants.

Hamas is clearly seeking to flex its muscles ahead of a potential new border agreement with Egypt that the militants hope will help end a two-year blockade.

The group called for a three-way meeting among Hamas, Egypt and the Fatah movement of Palestinian President Mahmoud Abbas, who controls the West Bank, to discuss a new border arrangement for Gaza.

"If the leadership in Ramallah refuses this call, we will not stand idle until the siege overruns life in Gaza," Hamas said in a statement.

The border breach provided a significant popularity boost to Hamas, which can claim it successfully broke through the closure that has deprived the coastal territory of normal trade and commerce.

"Hamas did this and when Egypt found resistance, it let up," said a joyous Reem Sahloul, 28, of Khan Younis. "Hamas proved stronger than the (Egyptian) army."

Egypt has rejected any suggestion of assuming responsibility for the crowded, impoverished territory -- a hot issue in light of comments this week by Israeli officials who said the border breach could relieve Israel of its burdens in Gaza.

Israel withdrew its troops and settlers from the territory in 2005, but it still controls access to Gaza, including Gaza's airspace and coastline. Israel also provides the fuel needed to run Gaza's only power plant. It has recently withheld that fuel, causing severe power outages.

In an interview published Friday, President Hosni Mubarak decried the situation in Gaza as "unacceptable" and called on Israel to "lift its siege" and "solve the problem."

"They should get things back to normal according to previous agreements and understandings," Mubarak told the weekly Al-Osboa.

He also invited rival Palestinian factions to Cairo for talks, but did not mention a date. Hamas spokesman Ayman Taha told Al-Jazeera TV that Hamas' supreme leader, Khaled Mashaal, was ready to accept the invitation. But Abbas' representative in Egypt, Nabil Shaath, said Fatah had made no decision.