Col. Moammar Gaddafi’s former intelligence chief was seriously injured while in the custody of Libyan revolutionaries, officials said Thursday, the latest in a string of murky incidents that have raised questions about retaliatory attacks against members of the old regime.

The cause of the injuries suffered by Abuzed Omar Dorda this week is disputed. One of his relatives said he was thrown from a second-story window by his jailers. Libyan militiamen gave conflicting accounts Thursday, blaming his fall on a suicide attempt or an effort to escape.

The incident underlined the haphazard nature of justice in post-revolutionary Libya, where about 7,000 prisoners of war are being held in makeshift detention centers. Dorda was being interrogated in the offices of a pasta factory controlled by a revolutionary brigade when he toppled about 30 feet from the window, the militiamen said. The elderly man fractured his hip, said doctors who treated him.

The incident occurred on Tuesday, five days after Gaddafi and his son Motassim died while in the custody of revolutionaries after being captured wounded. Under intense international pressure, the interim government has announced it will investigate the former leader’s death.

Libya continued to be transfixed by the fate of the hated Gaddafi family, with another of the late dictator’s sons, former top official Saif al-Islam, still on the run. Reuters reported Thursday that he had slipped over the border into Niger. Asked whether the interim government had confirmed that report, spokesman Jalal al-Gallal said, “Absolutely not.”

The U.N. Security Council adopted a resolution Thursday declaring an end to the no-fly zone it had established to protect the Libyan population as rebels struggled for eight months to vanquish Gaddafi and his supporters. But, reflecting mounting worry about post-revolutionary abuses, the resolution also urged Libya’s new government “to take all steps necessary to prevent reprisals, wrongful imprisonment and extrajudicial executions.”

Dorda had long been a high-ranking official, serving as Libya’s U.N. ambassador and director of external security.

Adel Khalifa Dorda, his son-in-law, appealed to U.N. Secretary-General Ban Ki-moon and the Security Council president to intercede with Libyan authorities to protect the former official. “Mr. Dorda survived a murder attempt . . . at the hands of his guards,” the younger Dorda wrote.

Ian Martin, the United Nations’ special representative for Libya, has instructed his staff to look into the claim.

The elder Dorda was taken to Mitiga military hospital in Tripoli, doctors said. Sadiq Turki, the militiaman in charge of the hospital, declined to allow a reporter to see him on Thursday, saying: “This is confidential.”

Doctors who treated Dorda said he had a fractured left hip and internal bleeding around the injury, and was being kept in the intensive-care unit. “His general condition is stable,” said Faraj al-Farjani, a surgeon.

Revolutionaries based at the Al-Jawda Macaroni Factory on the outskirts of Tripoli, where Dorda was injured, gave varying accounts of how he had plunged to the concrete pavement.

One, Marwan Ardawi, said that Dorda had been moved continually from house to house because of his importance. He was taken to the factory in the suburb of Ein Zara on Tuesday, and plummeted from the window at 5 p.m. during a break in his interrogation, Ardawi said.

“We heard him screaming. He fell from the second floor,” he said. Ardawi said Dorda apparently was trying to escape.

The factory is guarded by armed revolutionaries and surrounded by a concrete wall about 10 feet high topped with barbed wire, so it isn’t clear how Dorda might have fled even if he had survived the 30-foot jump unscathed. The revolutionaries, who are from the al-Rahebat brigade in the western mountains of Libya but have set up camp in Tripoli, showed a reporter the window but not the room where Dorda had been held.

Another revolutionary, who identified himself only as Saeed, told a reporter: “He tried to suicide.”

Turki, the hospital director, expressed contempt for Dorda. “He’s the one who gave orders to kill and rape in Tripoli,” he said. Adel Dorda insisted that his father-in-law had never committed atrocities.

Lynch reported from New York.