Jumping out of an Air Force plane flying high enough to avoid puncturing the nighttime silence, members of a Navy SEAL team parachuted into Somalia's darkness to rescue two aid workers, an American and a Dane, from their three-month captivity.

The operation, which unfolded early Wednesday local time in a remote region of Somalia, extracted the two hostages unharmed and left their nine captors dead, according to the U.S. military. It represented the first public report of an extended U.S. ground raid in that country since a 1993 operation in Mogadishu that left 19 American service members dead and prompted the U.S. to withdraw from Somalia.

The raid was planned and carried out after U.S. officials developed intelligence on the hostages' location and information that raised concerns about the deteriorating health of Jessica Buchanan, a 32-year-old American originally from Ohio. "There was a window of opportunity for military success," Navy Capt. John Kirby, the chief Pentagon spokesman, said Wednesday. "Within the last week or so, we were able to connect enough dots to make the decision."

The operation was the culmination of weeks of secrecy and strategy sessions among officials at the White House, the Pentagon and U.S. military commands abroad, according to defense and senior administration officials. The plan was propelled by the urgency of freeing Ms. Buchanan and Poul Hagen Thisted, a 60-year-old Danish man. Working for a Danish nonprofit group that removes land mines from conflict zones, the two were taken hostage Oct. 25, 2011, by gunmen with unknown motives.

The White House and top Pentagon officials tracked the situation from that day, officials say. On Nov. 23, the White House held a formal meeting of the national security staff to discuss it. Officials appear to have been uncertain then of where the two were being held. At that meeting, President Barack Obama directed that the efforts to find Ms. Buchanan continue, a senior administration official said.

By January, U.S. officials appear to have homed in on the location, near Gadaado, Somalia, east of the Ethiopian border. Last week, aides briefed Mr. Obama on new intelligence reports that Ms. Buchanan's health was deteriorating. Administration and military officials didn't provide details of Ms. Buchanan's health condition, citing privacy restrictions. Members of her family couldn't be located to comment Wednesday.

Don Meyer, the president of Valley Forge Christian College, the Pennsylvania school from which Ms. Buchanan graduated, said the college community was "grateful" for the rescue by the U.S. commandos. "I'm glad they are on our side," he said. John Brennan, the president's senior counterterrorism adviser, began providing Mr. Obama daily updates, noting that a rescue attempt was likely imminent.

To carry out any rescue, the military chose a commando team that included members of SEAL Team Six, the elite special mission unit that carried out the May 2011 raid into Pakistan that killed Osama bin Laden. On Saturday, senior national-security officials held a video teleconference to discuss rescue options, the senior administration official said. At a Monday evening meeting with Mr. Brennan in the White House residence, Mr. Obama authorized the operation.

On Tuesday evening in Washington, before leaving to watch Mr. Obama deliver his annual State of the Union address, Defense Secretary Leon Panetta watched the raid unfold on a video link at the White House. The Air Force provided overhead video of the raid as it unfolded, officials said. Across the world, an Air Force plane ferrying the commandos had taken off from an undisclosed location and flew over Somalia, close to the Ethiopian border. The commandos jumped out.

They were on the ground for about an hour. The SEALs found the encampment where nine armed men were holding the two captives. They reported that there were also explosives at the location. Military officials provided few details of the armed encounter, including how the hostages were being held or the details behind the fight that left the captors dead. Provisions had been made to detain anyone who surrendered but the SEAL team didn't take prisoners, defense officials said. After the team freed Ms. Buchanan and Mr. Thisted, Army helicopters landed to ferry the SEAL team and the rescued hostages to safety.

The president was told at 6:43 p.m. that Ms. Buchanan and Mr. Thisted had been rescued and were safe. At 9 p.m., as he entered the House chamber to deliver his address, Mr. Obama turned to Mr. Panetta to tell him, "Good job tonight." After the speech, Mr. Obama spoke with Ms. Buchanan's father to inform him of the successful rescue mission, administration officials said.

The first stop for the freed hostages was a U.S. base in nearby Djibouti, Camp Lemonnier. Military officials declined to say later whether the hostages remained there or were taken elsewhere, saying they were at a medical facility in the region.

For the military, Tuesday's raid represented something of a return to Somalia. Under the Bush and Obama administration, the military has conducted occasional strikes at suspected terrorists. But until Tuesday, there hadn't been a public report of an extended ground raid. U.S. ground forces have mostly steered clear of the country since 1993. That year, U.S. special operations forces trying to capture Somali warlords ended up battling militants in a clash that left hundreds of Somalis and 19 American service members dead.

Pentagon officials said they haven't confirmed whether the captors holding Ms. Buchanan and Mr. Thisted had direct ties to pirates, characterizing them only as criminals. Still, military officials said that some pirates move between trying to capture ships and other criminal activity.

Emmanuel Ksiangani, a senior researcher at the South Africa based Institute for Security Studies who monitors Somalia, said the raid was unlikely to deter kidnappers in that country, parts of which has been buffeted by waves of drought, famine and armed conflict over the last two years.

"This doesn't change the dynamic of these people having no other source of livelihood and so they will try again," said Mr. Ksiangani. "They will use this as a propaganda tool. Even if these were criminal elements, they will say they killed innocent people and try to capitalize on the deaths of Somalis to create resentment against the United States." Wall Street Journal.

—Solomon Moore contributed to this article.