RAFAH, Gaza Strip, (AP) – Egyptian riot police blocked Gazan cars from entering Egypt on Saturday, the fourth day of a border breach, after Hamas militants had cleared a path for vehicles to cross.

Dozens of riot police formed human chains, blocking two passages used by cars that had carried large numbers of Palestinians across the border. Several Egyptian armored vehicles took up positions to back up the troops.

Earlier in the day, Egyptian border guards had allowed the cars to pass. On Friday, the guards had made a failed attempt to stop the influx of Palestinians, then traveling on foot, 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 country’s border with Egypt, and that a road and several 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, and its 1.5 million residents, largely sealed off in the past two years, especially since the violent Hamas takeover of the territory in June.

On Friday, Egyptian riot troops using water cannons and dogs briefly tried to reseal the border, but were met by Hamas defiance. Militants driving a bulldozer knocked down more border barriers, including concrete slabs, under the watchful eye of Hamas security forces, and the Egyptians withdrew.

On Saturday, Gazans began driving into Egypt in large numbers for the first time, making it easier for them to stock up on supplies. Egyptian police set up several layers of checkpoints after the border, and Palestinians could drive no farther than El Arish, about 20 miles from the border. Those heading to El Arish, a resort town, had to use side roads because police had blocked the main road.

In the first days after the breach, most had crossed on foot.

The traffic initially flowed in both directions, before riot police stepped in to cut it off. 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.

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 is based in Ramallah and 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.