American troops caught in deadly Niger ambush told to proceed despite mission concerns The operation in Niger was a kill or capture mission.

 -- The operation in Niger that led to the death of four American soldiers was not a reconnaissance mission, as initially described by U.S. officials, but instead a kill or capture mission conducted without additional support requested by Nigerien forces, four senior Nigerien officials told ABC News.

The American team leader also expressed concerns about the mission, after a second U.S. and Nigerien unit was unable to join them for the operation, a senior U.S. intelligence source said.

While top Pentagon officials have described the mission as “reconnaissance,” local Nigerien military commanders said the Oct. 4 mission was always to kill or capture one of the most dangerous terrorist leaders in the country known locally as Dandou and code-named “Naylor Road” by the Americans.

Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford told reporters last week that the group of 12 U.S. and 30 Nigerien soldiers was on a "reconnaissance mission" when they were ambushed by about 50 ISIS-linked fighters outside the village of Tongo Tongo.

Dunford emphasized that the U.S. was in an "advise and assist" role when partnering with the Nigerien force, but multiple sources in Niger told ABC News that the mission was American organized and led from the start.

Dandou is believed to be responsible for a number of attacks in Niger and has ties to ISIS and al-Qaeda, ABC News has learned. Nigerien officials said they believe he was involved in the deadly ambush against U.S. troops that killed Staff Sgt. Bryan Black, Staff Sgt. Jeremiah Johnson, Staff Sgt. Dustin Wright and Sgt. La David Johnson.

Yet, even among American and Nigerien sources close to the investigation, there is discrepancy about the initial mission assigned to the team. While the Nigeriens insist it was “kill or capture” from the start, two U.S. intelligence sources told ABC News the team was first asked to meet local leaders and were only assigned the “Naylor Road” mission on their way back to base.

Either way, the team proceeded in search of the target’s campsite in an overnight raid. The change in plan meant the team was out for over 24 hours, potentially putting them at greater risk.

“They should have been up and back in a day,” a senior U.S. intelligence official told ABC News. “But they were up there so long on a mission that morphed, they were spotted, surveilled and ultimately hit.”

One Nigerien military officer told ABC News that this second phase of the operation led the group to the Niger-Mali border, a dangerous area known to locals as the "red zone." The U.S. State Department warned on Monday that "terrorist organizations, armed groups and smugglers" operate in the area.

Dunford, however, told reporters last week that leaders on the ground assessed enemy contact was unlikely during the mission.

A Nigerien officer said he asked for more soldiers and weapons to bolster the operation, but claimed that request was rejected by the American side.

And there were more concerns raised later in the day.

A second team, also comprised of American and Nigerien forces, was supposed to join the mission, but for reasons that remain unclear, they were unable to do so. While one U.S. official told ABC News that weather had grounded the team, another senior American source disputed that claim and said miscommunication may have been to blame.

The original 12-member team and their Nigerien partners were told to proceed on their own in a convoy of six to eight vehicles, one senior intelligence source said, despite concerns voiced by the American team leader.

The Americans were traveling in two pickup trucks with mounted machine guns and one unarmed Land Cruiser. A fourth vehicle, said to have been provided to the Nigeriens by the CIA, had specialized surveillance equipment on board.

Dunford said last week that he had no knowledge of CIA involvement.

At least one of the American trucks was captured by the attackers after the battle, as well as a vehicle provided by the CIA for the Nigeriens, multiple Nigerien officials said.

The CIA had no comment when asked by ABC News.

U.S. Africa Command (AFRICOM) provided the following statement: "As this incident remains under investigation, it would be inappropriate for AFRICOM to comment at this time."

Until the ambush, the mission had been unremarkable.

When the team reached their target, "Naylor Road"’s suspected camp, in the middle of the night they found it empty and burned its remains before getting back into their vehicles as the sun came up.

They drove south toward their base and stopped in the village of Tongo Tongo around mid-morning so the Nigerien forces could cook and eat breakfast. While there, the Americans met with a village elder, who they now believe was "obviously and deliberately trying to stall them," according to U.S. intelligence sources.

When they finally departed the village, they had not traveled more than the length of a football field before they were ambushed by what was described as a well-trained, seasoned force who used machine guns, mortars and rocket-propelled grenades.

The two American pickup trucks managed to get out of the line of fire, only to realize that the Land Cruiser was nowhere to be seen. Unable to reach them, some of the Americans went back on foot and in one of the pickup trucks to look for them while Johnson, who was later killed, provided cover by firing with the machine gun mounted on the back of the other pickup truck.

It was then that the Land Cruiser, containing the other three Americans killed, was hit by a mortar and then gunfire.

The Americans continued to fight from their vehicles and on foot. At some point, one of the U.S. pickup trucks was disabled.

Two hours later, after the first shots were fired and one hour after the Americans called for help, French Mirage jets buzzed low over the battle, causing the attackers to hold their fire and many retreated into the local population. French Puma helicopters, accompanied by a pair of American Green Berets, from Ouagadougou, Burkina Faso evacuated the wounded. Later, a U.S. contractor plane would take away the dead after Nigerien and American forces responded and secured the area.

According to the senior intelligence source, the body of Johnson was not located until two days after the attack. In circumstances that remain unclear he became separated from the rest of the group and his body was turned over by the village to the Nigerien military only as an American attack formation moved in to look for him, the source said.

ABC News' Luis Martinez, Aicha El Hammar Castano and Angus Hines contributed to this report.