The remote-controlled device exploded in Jalalabad as a vehicle passed carrying state prosecutor Abdul Qayoom, local government spokesman Ahmad Zia Abdulzai told AFP.
The powerful explosion in the city centre wounded Qayoom, his driver and four guards and 10 civilians, Abdulzai said.
A doctor at the city's main hospital said 16 people with bomb injuries were admitted and the condition of four, including the prosecutor, was "very serious".
There was no immediate claim of responsibility for the bombing, which followed a deadly suicide attack on the Indian consulate in the same city yesterday which killed nine civilians, most of them children studying the Koran in a nearby mosque.
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The Taliban and their Al-Qaeda allies are behind most of the bombings which have plagued life in Afghanistan since the ousting of the Islamists from power in a US-led invasion in late 2001.
The militants often deny attacks that cause high number of civilian casualties and exaggerate attacks on military targets.
India has been a key supporter of Kabul's post-Taliban government, and analysts have often pointed to the threat of a "proxy war" in Afghanistan between India and its arch-rival Pakistan.
New Delhi reacted to the consulate attack with thinly-veiled criticism of Pakistan for failing to crack down on militants and their safe havens along its western border.
The Haqqani network, a Pakistan-based group allied with Taliban and closely associated with the Pakistani intelligence service, was blamed for earlier attacks on Indian targets in Afghanistan.