Cowards or afraid to shoot fellow Muslims? Probably a combination of both.

KABUL, Afghanistan — Nazir Amini, an Afghan visiting from his home in Germany, had just returned from the buffet with a bowl of ice cream when two men with an AK-47 rifle and a machine gun started shooting guests around the pool at the Intercontinental Hotel, one of the capital’s most fortified buildings.

Women and children screamed. Chairs tipped backward. Food slid onto the lawn as people started to run. Mr. Amini said he saw police officers running, too, tightly gripping their own AK-47s as they raced away from the gunmen.

“I said, ‘Why don’t you shoot? Shoot!’” he recalled. “But they just said, ‘Get away from them.’ And we all ran together.”

Six hours later, at least 21 people were dead, including the nine suicide bombers who managed to penetrate several rings of security on Tuesday night to carry out the attack. The assault has shaken public confidence in the ability of Afghan forces, especially the police, to assume responsibility for security, even here in the capital.

The scene painted by Mr. Amini and several other guests at the hotel vividly demonstrated the challenges facing the Afghan government as it prepares to defend its country without NATO troops after 2014. Last week, President Obama announced that the American military had inflicted enough damage on the insurgency to allow him to begin withdrawing some troops. This week is supposed to be the beginning of the transition to Afghan control, with Kabul, one of the country’s safest cities, scheduled to be among the first places to carry out the transfer.