Palestinian militants forced open a border gate Friday between Egypt and Gaza, letting hundreds of people pour across despite warning shots from Israeli helicopter gunships.

At least 600 people — mostly students and patients trapped at the border in the weeks the Rafah crossing was closed — passed freely over the frontier. Six Palestinian militants stood by, periodically firing in the air, witnesses and Palestinian security said.

Also Friday, the United States pledged $50 million for Palestinian refugees, while Palestinian President Mahmoud Abbas urged Washington to pressure Israel to end its military offensive in the Gaza Strip.

Abbas told Secretary of State Condoleezza Rice in a telephone call that he was making every effort to end the Gaza crisis, the Palestinian leader's office said.

The United States donated the money to the U.N. Relief and Works Agency to aid Gaza Strip and West Bank residents impacted by the fighting, U.S. Assistant Secretary of State David Welch said after meeting Abbas on Friday.

Israel launched its offensive in Gaza after Palestinian militants tunneled under the border June 25 and attacked an Israeli army post, killing two soldiers and capturing a third.

The Rafah border crossing — Gaza's main gateway to the outside world — has largely been closed since then.

Masked Palestinian militants firing guns broke into the Egyptian side of the Rafah border crossing, clearing the way for the trapped Gazans, Egyptian police Capt. Mohammed Abdel Hadi said.

Militants from the ruling Hamas party said they opened the border gate as a "gift" to the Palestinian people.

Some people passed through the gate on crutches, even as they lugged suitcases. Others walked or ran. A handful of Palestinian cars were seen crossing into Egypt.

Fearful militants would use the open border to smuggle arms into Gaza, Israeli helicopters fired warning shots to stop people from crossing, the army said.

Egyptian police used tear gas and dogs to try to disperse the crowd, but the flow continued. Three Egyptian police were injured by Palestinian gunmen, the police said.

Rafah's closure stranded hundreds of Palestinians who work and study in Egypt, and prevented hundreds of others from leaving the coastal area to receive medical treatment. Last week, a 26-year-old Palestinian woman with cancer died at the border while waiting to cross.

Early Saturday, an Israeli airstrike targeted the Gaza City offices of the Palestinian economy ministry, setting the building on fire, Palestinian officials said. There were no immediate reports of casualties. The army said it attacked the ministry, which is controlled by the Hamas-led government.

On Friday, a Palestinian was killed when an Israeli tank shell hit his truck, hospital officials said, and Israeli aircraft struck targets in parts of Gaza.

Since the offensive began in Gaza, 86 Palestinians have been killed, many of them gunmen. The civilian victims included a 10-year-old Palestinian who died in a hospital Friday, four days after being wounded in Beit Lahiya, officials said.

An Israeli soldier also was killed during the offensive by friendly fire.