Taliban militants launched a grenade and gun attack on Kabul airport early Monday, taking over two nearby buildings which security forces attempted to storm as blasts and shooting rocked the Afghan capital.
Loud explosions and bursts of small-arms fire erupted for at least three hours after the US embassy sounded its "duck and cover" alarm and its loudspeakers warned that the alarm was not a drill.
"They have taken position in two buildings and have been shooting at the airport," Kabul police chief Mohammad Ayoub Salangi told AFP. "A car bomb that was left there has been defused.
"The remaining enemies are surrounded very tightly. People were rescued from the half-built buildings where the gunmen are holed up."
Three of the insurgents, who were armed with rocket-propelled grenades (RPGs) and machine guns, were killed by security forces as other attackers fought on.
"There are perhaps two to three others still there. They have taken buildings and have been firing from there," Sediq Sediqqi, spokesman for the interior ministry, told AFP. "Security forces are getting closer."
A Taliban spokesman claimed responsibility for the attack, which began at 4:30 am (1200 GMT). There were no immediate reports of casualties.
The heavily-guarded airport, which is both a civilian and military facility and contains a large base for the US-led NATO coalition, was closed to all flights.
The NATO coalition said that some international forces were involved in the military response.
"There were personnel from the International Security Assistance Force (ISAF) with Afghan forces, but Afghan forces led the operation," a coalition spokesman told AFP.
President Hamid Karzai was on a visit to Qatar but it was unconfirmed whether he was scheduled to return on Monday.
Kabul last came under attack on May 24, when Taliban militants launched a coordinated suicide and gun attack on a compound of the International Organization for Migration (IOM).
One insurgent detonated himself outside the compound at the start of the fighting, which left several buildings destroyed or damaged by rocket-propelled grenades, gunfire and explosions.
A policeman, two civilians and all four militants died in that attack, with the government lauding the response of the Kabul security forces for preventing further casualties.
The effectiveness of Afghan forces is crucial to the government's ability to defeat the Taliban insurgency as 100,000 NATO-led combat troops withdraw by the end of 2014.
The police, army and special forces are being trained by the international coalition, but there are widespread fears that they will not be able to impose security after 12 years of war.
On Saturday, an Afghan soldier shot dead two US soldiers and one US civilian, the latest "insider attack" to undermine efforts by the two armies to work together to defeat the Taliban insurgency.
The killings in the eastern province of Paktika came on the same day that one Italian soldier died when a grenade was thrown into an armoured vehicle in Farah province, in the far west of the country.
In another recent attack to shake confidence in Afghanistan's prospects after 2014, International Committee of the Red Cross (ICRC) offices in the eastern city of Jalalabad were attacked on May 29.
The two-hour assault, which left one Afghan guard dead, was the first time ICRC offices have been targeted in Afghanistan since the aid organisation began work in the country 26 years ago.
The Taliban, who were ousted from power in Kabul in 2001 for sheltering the Al-Qaeda militants behind the 9/11 attacks, have fought a long and bloody insurgency against Karzai's US-backed government.