Seven Afghan civilians nearby were injured by the blast which appears to have been detonated by remote control just seconds after a NATO vehicle passed. District Police Chief Mohammad Akber said the bomb was attached to a bicycle parked near a crowded market.
"It was at nine o'clock in the morning that a bomb placed on a bicycle exploded here at the Bazar wounding seven people -- four people inside a passing taxi and three people passing by this road," Akber said. "We are investigating at the moment."
A Taliban spokesman has claimed responsibility. Taliban attacks in Kabul are not common. But the city has seen periodic rocket attacks and bomb blasts since U.S.-led forces overthrew the fundamentalist Taliban government in late 2001.
Sam Zarifi, a researcher on Afghanistan for Human Rights Watch, said there are concerns about an increase in violence across Afghanistan during May.
"We've seen in the last few weeks an upsurge of violence in Afghanistan," Zarifi said. "We're not quite sure exactly what all the reasons for it are. But with the end of the cold season and with upcoming parliamentary elections, unfortunately, the outlook is that the violence could increase. So it's even more important than before for the United States and its allies -- NATO really, which has taken over responsibility for providing security in Afghanistan -- to step up to the plate (deploy more NATO troops) and to finally fulfill their commitments to Afghanistan."
Just a few months ago, before the spring thaw began in Afghanistan, U.S. military commanders were boasting that the Taliban was practically defeated and no longer posed a threat to the central government. Zarifi said there has been a tendency among U.S. officials to declare Afghanistan a complete success. And he said such declarations are premature.
"It's very clear that as the snows melted in Afghanistan and as the weather cleared up, there is some movement afoot," Zarifi said. "Whether it is for political reasons or economic reasons, the month of May just was a particularly bad month in Afghanistan after several months of relative quiet. The overall outlook for the summer has now been put into doubt."
Zarifi noted that it is not just the number of violent attacks that have been proliferating. He said the types of attacks also are increasing.
"We've seen in May a kidnapping and attempted kidnapping in Kabul of foreigners working there," Zarifi said. "We've seen a suicide bomb attack -- something really rarely seen -- which targeted an internet café where foreigners worked. We've seen protests that really rocked the country -- focusing on the southeast. But protests against the U.S. presence there. And we've seen some factional fighting again in the northern part of the country."
In fact, Zarifi said, factional fighting between local militia commanders could pose the biggest threat to parliamentary elections in much of Afghanistan.
"Because of the nature of parliamentary elections -- because of how intensely local they are and because of the role of the future parliament -- we expect these races to be very competitive in a lot of places in Afghanistan," Zarifi said. "With the presidential elections, there wasn't as much competition. And even then, we had some serious cases of intimidation and efforts to sway the vote one way or the other. We expect this to be much more serious with the parliamentary elections as different groups jockey for power."
Human Rights Watch has noted that at least one parliamentary candidate and former delegate to Afghanistan's recent Loya Jirga has been killed. Akhtar Mohammad Tolwak was killed along with his driver on 11 May while driving in the eastern part of Ghazni Province.
An Italian aid worker for CARE International has been a hostage since she was abducted from her car in central Kabul on 16 May. Earlier in May, armed men failed in their attempts to kidnap three foreign World Bank employees under similar circumstances in Kabul.
Periodic rocket attacks against foreign military bases in Kabul and Kandahar have continued after a lull during the winter.
At least 11 Afghan employees of a Washington-based agricultural firm were shot and killed by suspected Taliban fighters in Zabul Province during the last two weeks.
Human Rights Watch has called on the United States to lead efforts to speed the deployment of additional international security forces to remote Afghan provinces. The group also says there needs to be more international human rights monitors and election monitors for the parliamentary elections.