He said eight people were wounded in the attack.
There were two further attacks in Lashkar Gah, capital of the southern province of Helmand. In both cases the bombers killed themselves but no one else.
One attacker targeted a Nato convoy, but wounded two Afghan bystanders, according to Mohammad Isa Iftikhari, the deputy police chief of Helmand.
In the other attack, on an Afghan army office in the provincial capital, a soldier was wounded.
Last year saw the worst violence in Afghanistan since the Taliban was chased from power by US-led forces in late 2001.
More than 4,000 people died in fighting in 2006, including about 1,000 civilians. Suicide bombings jumped from 21 to 139.
Fighting is expected to be heavy in 2007 as the Taliban has announced it has prepared thousands of suicide bombers.
Ronald Neumann, the US ambassador to Kabul, said on Monday that US-led forces were fully capable of repelling the Taliban's spring offensive as circumstances are now less favourable for the fighters.
Nato and Afghan troops last week launched their biggest operation so far to pre-empt the Taliban's spring offensive.