A Taliban suicide attacker targeted an Afghan army bus in Kabul Thursday, killing three people.
The strike is the latest deadly attack against vehicles taking government staff to work in the Afghan capital.
At least eight people were wounded in the blast.
A day earlier, at least seven people were killed in two separate bomb blasts targeting busloads of soldiers also in the capital.
The Taliban has claimed responsibility for all three attacks.
Taliban spokesman Zabihullah Mujahid told the French News Agency Wednesday that the militants were sending a "clear message" to the Afghan government for its signing of a long-delayed security deal with United States, and that they would increase attacks.
On Tuesday, officials from Afghanistan and the United States signed a bilateral security agreement that will allow nearly 10,000 U.S. military and civilian personnel, and another 2,000 NATO forces, to stay after the original December 31 deadline for the international troops to exit.
The pact allows the foreign coalition to continue training Afghan security forces and targeting al-Qaida operations in the country.
The signing took place on newly-inaugurated President Ashraf Ghani's first day in office.