By Sanjeev Miglani and Mirwais Harooni
KABUL (Reuters) - Afghan security forces backed by NATO attack helicopters fought Taliban insurgents floor-by-floor in an unfinished high-rise in the center of Kabul on Wednesday, more than 15 hours after the biggest militant assault on the Afghan capital began.
It was not known how many fighters were still holed up in the 12-storey building near Kabul's diplomatic district from where they fired rockets at the heavily-fortified U.S. embassy and NATO headquarters as part of a coordinated attack targeting other areas of the city as well.
At least nine people were killed and 23 wounded in four attacks, and the ability of the Taliban to penetrate Kabul's vaunted "Ring of Steel" was a clear show of strength ahead of a handover of security to Afghan forces slated for 2014.
"Security forces are inside the building until the fifth floor, and insurgents are three floors higher. And foreign forces are trying to target the insurgents from helicopters," said Hashmatullah Stanikzai, a spokesman for the Kabul police chief.
A Taliban spokesman in a text message to Reuters said the attackers had enough ammunition to carry on fighting, in what is already the longest sustained attack on Kabul since the U.S.-led invasion a decade ago.
"The resistance is ongoing with full intensity," Zabihullah Mujahid said, adding the attackers had provided updates through telephone. "The fighters said they have enough ammunition to prolong the operation."
A squad of about five insurgents took over the shopping center under construction on the outskirts of Kabul's diplomatic district on Tuesday, armed with rocket-propelled grenade launchers, AK-47 assault rifles and suicide bomb vests.
"Forces are still working on clearing operations," a spokesman of the NATO-led International Security Assistance Force told Reuters early on Wednesday.
Explosions were interspersed with gunfire all afternoon on Tuesday and several rockets landed in the upmarket Wazir Akbar Khan district, near the British and other embassies. One hit a school bus but it appeared to have been empty at the time.
The gun battle that started around Abdul Haq square went on into the early evening, with three attackers killed and one or two still at large nearly eight hours after the assault began, the Interior Ministry said on Tuesday.
"The scale of today's attack is unprecedented," said Andrew Exum, fellow at the Center for a New American Security.
"There was almost certainly either a break-down in security among the Afghans with responsibility for Kabul or an intelligence failure."
On the day the attack started, a U.S. Senate panel approved a $1.6 billion cut in projected U.S. funding for Afghan security forces, part of a significant reduction in outlays for training and equipping Afghan army and police expected in the coming years.
The U.S. and British embassies and the NATO-led coalition said all their employees were safe.
Violence is at its worst since U.S.-backed Afghan forces toppled the Taliban government in late 2001, with high levels of foreign troop deaths and record civilian casualties.
The assault was the second big attack in the city in less than a month after suicide bombers targeted the British Council headquarters in mid-August, killing nine people.
In late June, insurgents launched an assault on a hotel in the capital frequented by Westerners, killing at least 10. But Tuesday's attack was even more ambitious.
(Additional reporting by Emma Graham-Harrison and Hamid Shalizi; Editing by Ed Lane)