Kabul has suffered a growing number of bombings by the Taliban and other militants as foreign combat troops withdraw from a 13-year-long war, leaving behind a smaller support mission.
Early on Tuesday, a remote-controlled bomb exploded on the city's outskirts as a bus carrying Afghan army personnel passed by, said Zahir Azimi, a spokesman for the Afghan defense ministry. Seven of the bus passengers were injured.
In an email to journalists, the Taliban insurgency claimed responsibility for that attack, Reuters reported.
A later blast shook houses in the Wazir Akbar Khan area of the city, which is home to embassies, international media offices and aid groups, but there were no casualties, police said.
"Someone threw a hand grenade and he was apprehended," said Sediq Sediqqi, a spokesman for the interior ministry. The suspect was being interrogated but his motive and target were still unclear, he added.
A day earlier, a magnetic bomb killed two US troops in the capital.