The American people and the fallen soldiers' families deserve answers about a deadly ambush in the African nation of Niger, the top U.S. general said Monday, without being able to provide many himself.

Three weeks after the attack by presumed Islamic State forces, Marine Corps Gen. Joseph Dunford, the Joint Chiefs of Staff chairman, said several matters must still be resolved. They include whether the United States had adequate intelligence and equipment for its operation, whether there a planning failure and why it took so long to recover one the bodies.

Dunford said four U.S. soldiers died after a battle that started Oct. 4 in a "complex situation," leading to a "difficult firefight." At a Pentagon news conference, he tried to outline what the military knows.

He said a group of 12 American forces accompanied 30 Nigerien forces to an area about 85 kilometers north of the capital on Oct. 3. When they sought the next day to return, they encountered about 50 enemy fighters traveling by vehicle, carrying small arms and rocket-propelled grenade launchers.

Within an hour of taking fire, the team requested support. Within another hour, a remote plane flew above. Later, French jets arrived and ferried wounded Americans to safety. The bodies of three American killed in the fighting were transported out of the battle scene, but one — Sgt. La David Johnson — was not recovered until Oct. 6.

Independent of the military's investigation, the Johnsons' ordeal has become a major political dispute in the United States after President Donald Trump credited himself with doing more to honor the dead and console families than any of his predecessors.

Then, Johnson's aunt said Trump showed "disrespect" to his family as he telephoned to extend condolences. In an extraordinary White House briefing, John Kelly, the former Marine general who is Trump's chief of staff, shot back at Trump's critics, and the president continued the criticism over the weekend.

Members of Congress are demanding answers almost three weeks after the ambush in a remote corner of Niger, where few Americans travel. Last week, Sen. John McCain, R-Ariz., the chairman of the Armed Services Committee, even threatened a subpoena to accelerate the flow of information from the administration.

Dunford said he and Defense Secretary James Mattis believe they are taking the proper steps to keep Congress informed of all actions, but if members feel differently, he will redouble his efforts to ensure they are satisfied with the information they get.

Dunford defended the broader American mission in Niger. He said U.S. forces have been in the country intermittently for more than two decades. Currently, some 800 U.S. service members are supporting a French-led mission to defeat the Islamic State, al-Qaida, and Boko Haram in West Africa.

Dunford said U.S. troops and forces from Niger set out with expectations that contact with the enemy was "unlikely" and that a probe into an ambush of the patrol, which left four U.S. special operations troops dead, may take weeks.

The patrol didn't seek additional support until about an hour after coming under attack, Dunford said, indicating the reasons for that delay would be among the topics of the inquiry. A U.S. surveillance drone arrived minutes later and French Mirage jets came on the scene after about an hour after the request for help and provided streaming video of the engagement, Dunford said.

U.S. lawmakers have questioned whether the troops that were ambushed had adequate support and whether there's been sufficient congressional review as the Trump administration backs more aggressive rules of engagement in Africa and in the broader fight against terrorist groups globally.

Dunford said about 800 U.S. troops operate in Niger in support of more than 4,000 French and 30,000 local soldiers. That is part of a U.S. force totaling about 6,000 troops in Africa. Asked if the U.S. presence in Niger is a sign of "mission creep" in the region, Dunford said, "With a relatively small footprint we are enabling local forces to deal with these problems before they become a threat to the American people."

He said the initial assessment is that the Americans were killed by a group affiliated with Islamic State, which is trying "to leverage local insurgencies." Five Nigerien troops also were killed in the ambush.

The general described operations like the one in Niger as a reminder that threats to the U.S. from terrorist groups haven't dissipated with the capture of the group's strongholds in Iraq and Syria. "We have to acknowledge that our work is not done, even with the fall of Mosul and Raqqa," Dunford said. "We are at an inflection point, not an endpoint."

The Senate Foreign Relations Committee has scheduled a hearing with Defense Secretary Jim Mattis and Secretary of State Rex Tillerson on Oct. 30 to explore whether the expanding U.S. operations against terrorism require a new congressional authorization for the use of military force.

Dunford acknowledged "there's been a lot of speculation about the operation in Niger, and there's a perception that the Department of Defense has not been forthcoming." He said information would be be made public once the facts are determined and the families of the fallen soldiers are informed.

Despite a state of emergency, the closing of markets and a night ban on motorized traffic, there have been almost 50 militant attacks in Niger's two southwestern regions since February last year, according to the United Nations humanitarian office. The jihadists are often believed to come from neighboring Mali.

Dunford said an investigation is underway into what happened. He said the mission was originally set based on an assessment they were "unlikely" to come into conflict with any local forces.

"They did not expect resistance on their particular patrol," he said.

Dunford also said, based on what investigators know so far, the patrol did not call for support until one hour after being attacked, suggesting perhaps they believed they could handle the situation.

"We mitigate the risk to the US forces with specific guidance that we will only accompany those [local] forces when the prospects of enemy contact is unlikely."

Dunford said the clash reflects the globalization of the fight against the Islamic State group as it is driven out of key bases in Syria and Iraq.

"We are dealing with a challenge that exists from West Africa to Southeast Asia. . . . We're dealing with a global challenge," he added.

"That's exactly why we are conducting the kind of operations that we are conducting in Niger."

As to statements by Johnson's widow, Myeshia Johnson, that she asked to see her husband's body but was not allowed to do so, Dunford said the Pentagon does sometimes recommend the family not view remains of soldiers killed in action, but that Pentagon policy is for the family to decide.

The Associated Press, Reuters, Bloomberg, and Agence France-Presse contributed to this report.