A large blast that was most likely a suicide bomb attack ripped through the heavily barricaded diplomatic area of the Afghan capital Kabul, a police official said, and there were an unknown number of casualties.
At least two people were killed along with two suicide bombers, two people were also injured.
The guards fired on the assailants, killing them, but not before one of the vests exploded, said General Mohammad Daoud Amin, the deputy provincial police chief.
"Around 8 o'clock today there appeared to be a suicide bomb attack ... We cannot say what the target was at this point in time," Hashmatullah Stanikzai, a spokesperson for Kabul Police, said on Wednesday.
Embassy sirens sounded and ambulances could be heard after the blast, which happened in the area where the US and British embassies and the headquarters of the NATO-led International Security Assistance Force (ISAF) are located.
A spokesperson for ISAF said the coalition was aware of an explosion.
The blast reverberated around Kabul's Wazir Akbar Khan neighborhood. An alarm started going off at the nearby US Embassy, warning staff to take cover.
The neighborhood also is home to many high-ranking Afghan officials, international organisations and the headquarters of the international military coalition.
The Taliban claimed responsibility for the bombing in an email to reporters.
Wednesday's bombers were also armed with grenade launchers, said Amin, the deputy police chief.
He said they were stopped near a building that was under construction near the US base.
An international coalition vehicle was also damaged in the attack but there were no initial reports of casualties among the foreign forces, said Jamie Graybeal, a NATO troops spokesman.
The attack came as foreign and Afghan forces tightened their watch over the capital ahead of the holy day of Ashoura on Saturday, when Shia Muslims commemorate the seventh century death of Hussein, the grandson Prophet Muhammad.
Last year, the commemoration saw the first major sectarian attack since the fall of the Taliban regime.
In that strike, a suicide bomber on foot detonated his vest amid scores of worshippers at a Shia shrine, killing 56 people and wounding more than 160 others.
Police had already set up extra checkpoints around Kabul and specifically near shrines to search cars and people in the run up to the Ashoura.
On Tuesday, Amin said that all his forces were ``in the first security alert position'' and doing their "best to provide good security and prevent any possible incident on Ashoura."