Egypt said Wednesday it had found an arms-smuggling tunnel under the Gaza (search) border, and Palestinians crossing the frontier were warned to return by sunset when passport controls will be reimposed.

Egyptian border guards discovered the tunnel in the al-Duhniya (search) area, 2 1/2 miles south of the Rafah crossing point, on Tuesday evening, a security official said.

The tunnel contained 38 firearms and three rocket-propelled grenades, the official added, speaking on condition of anonymity because he was not authorized to speak to the press.

The tunnel penetrated to the Palestinian side of the frontier, and Palestinian security forces seized the weapons Wednesday, the official said.

The smuggling of weapons from Egypt (search) was a major concern of the Israeli military administration that ruled the Gaza Strip from 1967 until Monday. The Israeli withdrawal was conditional on Egypt's deploying troops along the border to prevent arms smuggling.

Meanwhile, Palestinian security forces stationed on the frontier warned people Wednesday that their three days of unimpeded crossings would end at 6 p.m. (11 a.m. EDT). Since the Israelis withdrew Monday, tens of thousands of Palestinians in Gaza have crossed the border to see relatives who live on the Egyptian side and to shop for goods that tend to be cheaper in Egypt, such as cigarettes, children's formula, cheese, gasoline and detergent.

"Anyone found on the Egyptian side after 6 p.m. will be considered an infiltrator," a Palestinian border guard said in a message blared through loudspeakers.

Late Tuesday, the Palestinian Authority warned that normal immigration controls would be imposed on Wednesday evening.

The crossing to Egypt is Gaza's only land link to the outside world that does not pass through Israel.