KABUL, Afghanistan — Afghan officials vowed Wednesday that a terrorist attack on one of the capital's best-known hotels wouldn't disrupt plans for the country's police and military to assume responsibility for security next month in seven key areas, including Kabul.

Opening a two-day conference of hundreds of Afghan officials to discuss the security handover, Dr. Ashraf Ghani, the government's point man on the transition, called the security change "irreversible." He said the Afghan government was undeterred by Tuesday night's attack on the Kabul Intercontinental hotel, which killed 12 civilians and police officers. The nine attackers also died.

"Our enemies should understand that they do not have the ability to block our national intentions," Ghani told delegates only hours after the six-hour hotel siege had ended at around 3:30 a.m.

The opening of the conference underscored the government's determination that the security change go ahead as scheduled. The meeting had been planned for the Intercontinental, but Afghan officials moved it to a government media center and proceeded as if Tuesday's attack hadn't happened.

Taliban spokesman Zabiullah Mujahid, in claiming credit for the attack, said that a reception for the conference's estimated 300 delegates had been the target. But a hotel employee who was working the front desk told McClatchy that only 30 to 40 of the delegates had arrived when the Taliban gunmen burst into the lobby at about 9:30 p.m.

The road to the hotel remained blocked Wednesday and Afghan officials provided scant details of the attack. The Interior Ministry put the death toll at 21, saying that nine Afghan civilians, most of them hotel workers, a Spanish national and two policemen had been killed by the insurgents, all nine of whom died, either suicides or by gunfire from Afghan police or two NATO helicopters that opened fire on the hotel roof to end the siege.

Unexplained, however, was how the attackers had gained entrance to the hotel, which is one of the most fortified buildings in the city, with multiple layers of security at its main entrance. The hotel worker told McClatchy he thought they'd come through the building's less well-defended rear door after one of the attackers blew himself up at the lone checkpoint there.

The security failing set off fierce debate over whether Afghan officials have the wherewithal to assume security responsibilities in the capital and six other areas, a handover that's expected to take place July 20.

"Our intelligence organizations can't figure out where an attack is going to happen. It shows their weakness," said Noorullhaq Ulomi, a former parliamentarian and military commander from Kandahar.

Ulomi said that however the Taliban had entered the hotel, their success underscored a lack of imagination on the part of Afghan security officials. A highly publicized gathering of top national and provincial officials to discuss the security handover was an obvious potential target.

"At such a sensitive time, when there are preparations for a security transition, our security forces must be fully vigilant," he said.

Others suggested it was likely that the Taliban had inside information about arrangements at the hotel, where the conference was to have brought together military advisers and governors from the seven cities and provinces where the security transition is to take place.

Abdul Wahid Taqat, another military expert, said the hotel presented government officials with two equally unpleasant scenarios: Either the attackers had inside information about the hotel's security arrangements from senior government officials or they had sympathizers within the security forces who allowed them to gain entrance to the hotel.

Taqat said he believed that Afghan intelligence organizations had known that Taliban insurgents were in the city planning an attack.

"Our security forces had the intelligence that 10 terrorists had entered the city," he said. "And still they could not prevent it."

(Shukoor is a McClatchy special correspondent.)

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