Medecins sans Frontieres (MSF) says a US attack on its clinic in the Afghan city of Kunduz killed at least 42 people - far more than first reported.
The medical charity had earlier said at least 30 people died in the 3 October attack by a US military gunship.
MSF said the figure was revised after a detailed investigation, complicated by the extensive damage to the clinic.
A US military inquiry said the attack was the result of "human error" but MSF has called it a war crime.
The charity is campaigning for an independent international inquiry into the bombardment, which took place as US-backed Afghan forces were battling to reverse the Taliban's seizure of Kunduz.
A statement released by MSF on Saturday said the dead included 14 staff members, 24 patients, and four relatives of patients who were helping in their care.
The charity said it had carried out extensive efforts to identify the dead, interviewing staff members and patients and checking figures with other hospitals that treated MSF patients following the attack.
Many records held at the clinic had been destroyed in the initial attack, the charity said, and human remains had been found in the rubble of the hospital over the past two months.
The US military's investigation into the attack, released on 25 November, concluded that the crew of the AC-130 gunship mistook the clinic for a nearby government building that had been seized by Taliban fighters.
The gunship fired 211 shells at the MSF compound over 25 minutes, the US military said, insisting that the attack was a "tragic mistake".
Shortly after the incident, the medical charity disputed initial US justifications for the attack, which said US forces had struck the hospital because they had come under fire in the area.
Meanwhile, a UN report has concluded that at least 289 Afghan civilians were killed and 559 wounded during the Taliban's brief seizure of Kunduz in September, and the campaign to retake the northern city.
The report detailed a climate of chaos in the city, with food shortages and allegations of human rights abuses by fighters on both sides.
Differing US statements on hospital strike
Saturday 3 October - Col Brian Tribus, spokesman for US Forces in Afghan
US forces conducted an airstrike in Kunduz city at 2:15am (local), Oct 3, against individuals threatening the force. The strike may have resulted in collateral damage to a nearby medical facility. This incident is under investigation.
Sunday 4 October - Pentagon press office
US forces conducted an airstrike in Kunduz city at 2:15am (local), Oct 3, against insurgents who were directly firing upon US service members advising and assisting Afghan Security Forces in the city of Kunduz. The strike was conducted in the vicinity of a Doctors Without Borders medical facility.
Monday 5 October - Gen John Campbell, US military chief in Afghanistan
We have now learned that on October 3, Afghan forces advised that they were taking fire from enemy positions and asked for air support from US forces. An airstrike was then called to eliminate the Taliban threat and several civilians were accidentally struck. This is different from the initial reports, which indicated that US forces were threatened and that the airstrike was called on their behalf.
Tuesday 6 October - Gen John Campbell to the Senate committee
On Saturday morning our forces provided close air support to Afghan forces at their request. To be clear the decision to provide aerial fires was a US decision, made within the US chain of command. A hospital was mistakenly struck. We would never intentionally target a protected medical facility… I assure you that the investigation will be thorough, objective and transparent.
Wednesday 25 November - Gen John Campbell statement
The US strike upon the MSF Trauma Centre in Kunduz... was the direct result of human error, compounded by systems and procedural failures. The US forces directly involved in this incident did not know the targeted compound was the MSF Trauma Centre. The medical facility was misidentified as a target by US personnel who believed they were striking a different building several hundred meters away where there were reports of combatants.