U.S. Central Command said its "early casualty reports" on what appeared to be the same incident gave lower figures: one civilian killed and six people injured, including a U.S. soldier. But the command said the investigation was not complete.
Among the wounded are a brother and son of Massoud Barzani, head of the Kurdistan Democratic Party, which runs half the Kurdish autonomy zone.
Other senior Kurdish military commanders - Saeed Abdullah, Abdul Rahman, Mamasta Hehman and Mansur Barzani, the political leader's son - also suffered injuries.
U.S. Special Forces have been working alongside Kurdish fighters, helping plan the assault against Iraqi forces in the north and calling in airstrikes to support the Kurds' advance into Baghdad-controlled territory.
Sunday's friendly fire deaths underscore the heightened intensity of combat along the northern front.
"There is more tension as this front becomes more active in order to put more pressure on the Iraqi side," said Hoshyar Zebari, a senior member of the KDP leadership.
Zebari said the "tragic" bombing along battle lines southeast of Irbil killed at least 17 Kurdish fighters and a translator for the British Broadcasting Corp., which was following the convoy. The injured was a roster of some of the KDP's top military officials.
Wajy Barzani, the Kurdish special forces commander and younger brother of Massoud Barzani, is in critical condition and was airlifted by U.S. forces to a hospital in Germany.
Massoud Barzani and the entire top ranks of his party's leadership are at the hospital, guarded by hundreds of Kurdish militiamen. Throngs of onlookers pressed forward, making it difficult for ambulances to pass. U.S. servicemen also arrived with vehicles, but it was unclear whether they carried any victims.
Zebari said the mistaken bombing could have been caused over a confusing and changing battle scene between Pir Dawad and Dibagah, 25 miles southwest of Irbil.
Kurdish and U.S. forces called for close air support after a column of Iraqi tanks tried to turn back advancing coalition soldiers. The convoy was near disabled Iraqi tanks when it was struck, he said.
The warplanes may have "mistaken some of the tanks that the (Kurdish fighters) had taken with the new column of tanks," he told reporters. "This was a war situation and these things happen."
The U.S. statement differed slightly on the location of the incident, placing it 30 miles southeast of Mosul, near Kalak. Kalak is 40 miles northwest of Dibagah.
It was not clear whether the convoy was on the front line of fighting or behind the most forward positions. Hours after the bombing, the Iraqi forces were pushed back at least 200 yards beyond the wreckage.
Driving Iraqi troops from Dibagah would cut off the main road connecting the main northern cities in Baghdad hands: Mosul and the Kirkuk oil center.
At the scene, BBC correspondent John Simpson reported that the convoy contained eight to 10 cars, two of which carried U.S. Special Forces troops. BBC translator Kamaran Abdurazaq Muhamed, who had been working for the corporation since mid-March, died in the bombing from blood loss after losing his legs.
"This is just a scene from hell here," Simpson said. "All the vehicles are on fire, there are bodies burning all around me, bits of bodies all around. ... The Americans saw this convoy and they bombed it. They hit their own people."
"I saw people burning to death in front of me," reported Simpson, who suffered minor shrapnel wounds.
Zebari stressed that the incident would not undercut Kurdish military and political backing for the coalition effort to topple Saddam Hussein.
"It will not affect ... our resolve to work together," Zebari said.
The Kurds, who live in Iraq, Turkey, Iran and parts of Syria, have long struggled to set up an independent state.
The foreign ministers of Iran and Turkey met Sunday and voiced opposition to the creation of a Kurdish state in northern Iraq. Turkey in particular fears that a Kurdish rebellion in Turkey could be re-ignited if Iraqi Kurds gain independence. The United States has said it seeks to keep Iraq intact.
Turkish Foreign Minister Abdullah Gul said he planned to travel next week to Syria to discuss the regional repercussions of the Iraq war.
By Brian Murphy