SAN’A, Yemen (AP) — Nearly 87 civilians were killed in a strike by government warplanes that hit a camp of people fleeing fighting in northern Yemen, a tribal leader said Thursday. It was a sign of increasing bloodiness in a remote war against Shiite rebels in this turmoil-ridden Arab nation.

The Yemeni government has said it is determined to stamp out the nearly 5-year-old rebellion, despite U.S. pressure for it to do more against al-Qaida, which has been strengthening its presence in the country.

Every day, warplanes screech over the ornate mud-brick skyline of San’a, the capital, to bomb the Shiite rebels in the northern region of Saada, on the border with Saudi Arabia. Some 150,000 Yemenis have fled their homes in the past five years, cramming into camps, schools and barns as aid groups struggle to bring in supplies.

On Wednesday, government jets bombed a makeshift camp packed with displaced people near the front-line town of Horf Sufyan, witnesses said. Sheik Mohammed Hassan, who attended a mass funeral for the victims Thursday, put the death toll at 87, most of them women and children.

The strikes hit near a school as well as a bridge under which many had taken shelter from the bombardment, crushing them, said Hassan, who is a member of the pro-government Sufyan tribe in the area and was among local leaders who organized the funeral. Tractors dug a trench in the area in which the dead were buried. Some of the bodies, torn apart in the blasts, were wrapped in plastic sheets, said a witness at the scene, who spoke on condition of anonymity because of fears of trouble with the government.

Government officials have refused to confirm the strike and none attended the funeral. Yemen’s Supreme Security Committee, which is headed by President Ali Abdullah Saleh, ordered an investigation into the reports, the state news agency SABA reported. It cited an unidentified official from the committee saying, rebels “have increasingly prevented civilians from moving to secure areas, using them as human shields”

In Geneva, the U.N. refugee agency expressed alarm over the reports. In a statement, the UNHCR said it “again strongly urges all parties to the conflict to ensure the safety and well being of the civilian population.”