The assault force, which also included elite troops from the United Arab Emirates, quickly found itself under intense fire from all sides — even from female combatants who unexpectedly took up weapons from assigned fighting positions — forcing the Americans to call in strikes from helicopter gunships and attack planes.
A Pentagon spokesman, Capt. Jeff Davis, denied on Thursday that the mission had been compromised.
On Wednesday, Mr. Trump flew to Dover Air Force Base in Delaware to be present as the body of the American commando killed in the raid, Chief Petty Officer William Owens, was returned home. It was the first military death on the new commander in chief’s watch.
Mr. Spicer insisted on Thursday that the commandos had accomplished their mission, even though “it is tough to ever use the word ‘success’ when you know that somebody has lost their life.”
His explanation did not quell calls from human rights groups and at least one Democratic member of the House Armed Services Committee for an investigation into the mission and the allegations of civilian casualties. The Central Command said on Wednesday that civilian casualties were likely and that it was investigating.
According to Al Qaeda’s branch in Yemen, the dead include the 8-year-old daughter of Anwar al-Awlaki, the American-born Qaeda leader who was killed in a targeted drone strike in 2011.
Planning for the mission started months ago, Mr. Spicer said. On Nov. 7, the Central Command submitted its plan to the Pentagon for review. The Defense Department approved it on Dec. 19, and the plan was sent to Mr. Obama’s National Security Council staff.
On Jan. 6, a meeting of senior Obama security aides, called the deputies committee, recommended that the plan go forward, Mr. Spicer said. Military officials have said that Mr. Obama did not act because the Pentagon wanted to launch the attack on a moonless night, and the next one after the meeting would come after Mr. Obama’s term had ended.
On Jan. 24, shortly after taking office, Defense Secretary Jim Mattis read the plan and sent it back to the White House with his support. On Jan. 25, Mr. Trump was briefed by his national security adviser, Michael T. Flynn, on the plan and on Mr. Mattis’s endorsement.
Mr. Trump summoned Mr. Mattis to dinner at the White House that night, along with Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, and Mr. Flynn. Also attending were two of Mr. Trump’s closest advisers, Jared Kushner and Stephen K. Bannon, as well as Vice President Mike Pence and Mike Pompeo, the C.I.A. director.
“The operation was laid out in great extent,” Mr. Spicer said. “The indication at that time was to go ahead.”
On Jan. 26, last Thursday, Mr. Trump formally signed the memo authorizing the action, Mr. Spicer said. Mr. Mattis and other aides updated the president on the raid throughout the night Saturday, Mr. Spicer said.
Members of Mr. Obama’s national security team pushed back Thursday at Mr. Spicer’s description of how the former president had set the stage for the decision. They said the attack had not been approved by Mr. Obama, and that materials left for the Trump team emphasized considerable risks.
“Not what happened,” Colin Kahl, the national security adviser to former Vice President Joseph R. Biden Jr., wrote on Twitter after Mr. Spicer’s briefing.
Mr. Kahl’s colleagues said that Lisa Monaco, Mr. Obama’s homeland security adviser, told the national security staff in early January that Mr. Obama was not prepared to approve the concept for the raid. Instead, they prepared a memorandum for Mr. Trump’s team that described a variety of options, and underscored the risks.