Police said the grenade was thrown from a speeding vehicle, and no one has claimed responsibility yet. A massive manhunt has been launched to track down the culprits.
The attack came hours after two grenades were lobbed at the Ministry of Women's Affairs and on a deserted street in the capital Kabul. No one was hurt.
The government of President Hamid Karzai says the Taliban and Al Qaeda activists are behind the recent blasts across the country, and that it is aimed at deterring or delaying the proposed deployment of NATO troops in the southern provinces of the country.
Karzai has publicly charged Pakistan with sheltering terrorists who strike on Afghan territory, a charge which Islamabad denies.
Islamabad, in turn, resents the growing Indian presence and clout in Afghanistan and believes that the Indian consulates in eastern Afghan cities of Jalalabad, Herat, Mazar-e Sharif, and Kandahar are being used to spy on Pakistan and foment trouble on its western borders.
In August 2003, a grenade was thrown at the Indian consulate building in Jalalabad.