Gunmen who stormed a hospital in the Afghan capital this week had come to "kill the mothers," a medical charity said, as survivors expressed shock and horror at the gruesome attack.

At least 24 people were killed -- including newborns, mothers and nurses -- when three armed men rampaged through the maternity ward of the Barchi National Hospital in Kabul on Tuesday, in an attack that sparked international outrage.

The United States later said the deadly assault was carried out by the Islamic State group. "What I saw in the maternity hospital demonstrates it was a systematic shooting of the mothers," said Frederic Bonnot on Thursday, the Doctors Without Borders (MSF) head in Afghanistan, who visited the facility a day after the attack.

"They went through the rooms in the maternity, shooting women in their beds. It was methodical. Walls sprayed with bullets, blood on the floors in the rooms, vehicles burnt out and windows shot through," he said in a statement.

MSF, which runs the maternity ward at the hospital, said at the time of the attack 26 mothers were being cared for at the Barchi National Hospital in west Kabul. Eleven were killed, including three in the delivery room with their newborn babies while five others were wounded.

Ten others found shelter in "safe rooms", which are common in Afghanistan and are often armoured to protect the occupants from gunfire or rockets.

Wrapped baby in scarves

One pregnant woman who hid in a safe room gave birth to a baby as gunmen went from room to room killing those who came in their way, a survivor of the attack told AFP on condition of anonymity. "We helped her with our bare hands, we had nothing else in the room except some toilet papers and our scarves," said a midwife who helped deliver the baby. "When the baby was born, we cut the umbilical cord using our hands. We used our headscarves to wrap the baby and the mother."

The assailants who entered the facility through the main gate moved straight to the maternity ward, MSF said. When the attack began, shooting and explosions could be heard from the safe room where several had taken refuge, said Bonnot.

"They came to kill the mothers," he added. "This country is sadly used to seeing horrific events. But what happened Tuesday is beyond words."

Officials said there were three attackers who were eventually killed in a lengthy clearance operation. Heavily armed security forces were seen carrying infants -- at least one wrapped in a blood-soaked blanket.

IS has not claimed the attack but US Special Representative to Afghanistan, Zalmay Khalilzad, said it was carried out by the Islamic State in Khorasan, the Afghan branch of IS. The Islamic State group "opposes a peace agreement between the Islamic Republic of Afghanistan and the Taliban, and seeks to encourage sectarian war as in Iraq and Syria," Khalilzad wrote on Twitter.

The Taliban has denied any involvement in the onslaught. In another attack on Tuesday in the country's east, a suicide bomber blew himself up at a funeral, killing at least 32 mourners, with IS later claiming responsibility. President Ashraf Ghani has blamed the Taliban for Tuesday's attacks, and ordered security forces to switch to an "offensive" footing against the militants. The Taliban, in response, vowed to fight back.

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