The US military may have purposely targeted a hospital in Afghan's Kunduz city, killing 22 people including 12 medical staff of the Medecins San Frontieres (MSF) or Doctors Without Borders, according to a report by the Associated Press.

Citing intelligence reports, AP said the MSF-run hospital had been under investigation by US Special Operations analysts several days prior to the Oct. 3 attack because the facility was believed to have been used as a base of operations by a Pakistani agent who was apparently coordinating Taliban activities.

The source also claimed that the hospital was used as a Taliban command and control centre and a storehouse for heavy weapons.

But no evidence has reportedly surface publicly suggesting a Pakistani died in the attack, according to AP. MSF officials also assured that none of its staff was Pakistani. It was reportedly a calm night and no fighting in or from the compound was happening prior to the airstrikes.

"What the new details suggest is that the hospital was intentionally targeted," said Meinie Nicolai, president of the operational directorate of MSF.

"This would amount to a premeditated massacre... Reports like this underscore how critical it is for the Obama administration to immediately give consent to an independent and impartial investigation by the International Humanitarian Fact-Finding Commission to find out how and why US forces attacked our hospital," she added.

President Obama earlier apologised to the MSF, but the group is calling for an international probe.

Gen. John Campbell, the top US officer in Afghanistan, had also acknowledged before the US Congress that the strike was a mistake, but he failed to clearly explained how it happened or who granted final approval.

The US and Afghan governments have already launch three separate investigations into the incident.

The MSF earlier condemned the bombing as a war crime. MSF officials insisted that no gunmen, weapons or ammunition were in the building prior and during the day of the attack.

The airstrike came as US advisers were helping Afghan forces take Kunduz back from the Taliban, which had seized the city.

MSF said US airplanes made five separate strafing runs over an hour, directing heavy fire on the main hospital building, which contained the emergency room and intensive care unit, said AP.

Meanwhile, a US military tank reportedly destroyed potential evidence when it forced its way onto the ruined site of a hospital run by MSF that was bombed by the US air force in Afghan's Kunduz city weeks ago.

Members of a joint investigation team from the US, NATO and Afghan government were believed to be onboard the heavy military vehicle which forced its way through the closed main gate compound around 1:30 p.m on Thursday last week (5 a.m, ET), according to Reuters, citing members of the MSF.

"Their unannounced and forced entry through the gates damaged property, destroyed potential evidence and caused stress and fear for the MSF team,'' the organisation said in a statement.