KABUL, Afghanistan (CNN) -- A NATO team arrived in northern Afghanistan late Friday night to investigate an airstrike that killed at least 90 people, a military spokeswoman said.
A victim of an ISAF airstrike on a hijacked oil tanker is carried into the Kunduz hospital on Friday.
A mix of Taliban militants and civilians were killed in the attack, NATO and local officials said.
The NATO team will work with Afghan investigators, said Capt. Elizabeth Mathias of NATO's International Security Assistance Force.
The airstrike occurred Thursday after fuel trucks were hijacked by militants in the Kunduz province. The trucks were carrying fuel for NATO forces when they were commandeered. At some point before the airstrike, people tried to empty fuel from the tankers.
Local Afghan officials were quoted as saying in some news reports that nearly half the people killed in the airstrike were civilians who rushed the fuel trucks. Mathias has declined to confirm that number.
Investigators will try to determine who was at the site and whether a mistake was made, Mathias said. Watch more about the airstrikes »
"Because of the prevalence of reports of civilian casualties, we don't want to be seen as ignoring the situation," Mathias said. "We don't want to wait. If something happened, we want to apologize."
Gen. Stanley McChrystal, the top U.S. commander in Afghanistan, is following the investigation, his public affairs officer, Lt. Col. Tadd Sholtis, said in an e-mail.
"He takes the possible loss of any innocent life seriously, and while he will not rush to judgment on the facts, he is following the investigation very closely," Sholtis said.
Brigadier General Eric Tremblay released a statement that said, "ISAF will do whatever is necessary to help the community, including medical assistance and evacuation as requested. ISAF regrets any unnecessary loss of human life, and is deeply concerned for the suffering that this action may have caused to our Afghan friends." See images of the strike aftermath »
Afghan President Hamid Karzai said he was "deeply saddened" by the deaths and reiterated that no civilians should be killed or injured in anti-terrorist military operations.
Sholtis said McChrystal "has been in touch with President Karzai and leadership of the major ministries on the incident."
Karzai's office issued a statement saying he had ordered a delegation to the area to investigate the incident and report back to him as soon as possible. The delegation includes representatives of the Ministry of Interior Affairs, National Directorate of Security, and the Provincial Administrative Department, according to the statement.
A spokesman for the provincial governor, Mahboobullah Sayeedi, said more than 90 people were killed.
The fuel trucks were hijacked late Thursday in Kunduz province and were spotted several hours later on the banks of the Kunduz River, ISAF said.
The hijacked vehicles became stuck in the Chardara area of the Ali Abaad district while trying to cross the river, according to Sayeedi. Militants had commandeered the trucks, which were carrying fuel for NATO forces, he said. People tried to empty fuel from the tankers when they couldn't go any farther.
With the trucks stuck on the riverbank, the German commander of the NATO forces called in the airstrike around 2:30 a.m., the German military said.
No German soldiers or planes were involved in the airstrike, but a German patrol made it to the site about 10 hours after the attack and came under small-arms fire, the German military said. The patrol continued its investigation Friday afternoon.
Meanwhile, a Polish soldier died in a roadside bombing on Friday in eastern Afghanistan, the Polish Defense Ministry confirmed.
Troops from a logistics convoy had been returning to a base, according to the Polish Defense Ministry. Five other soldiers were wounded in the attack.
Polish National Defense Minister Bogdan Klich issued a message of condolences and sympathy to the wounded in the Defense Ministry statement.
NATO's International Security Assistance Force reported the same incident in a Saturday news release, but did not release the nationalities of the victims.
It is the sixth ISAF death since the start of September, and the 11th Polish service member killed in the Afghan conflict.