At least two armed Taliban fighters equipped with suicide vests attacked a government building in the southern province of Kandahar on Monday, a police official said.
A provincial police official told the German Press Agency dpa that least one of the bombers detonated his explosives in front of the intelligence service's office in the centre of Kandahar city, while the other was still exchanging fire with security forces.
There were no reports of casualties, the official, who did not want to be named, said.
Gunfire was also heard near the provincial council's office, he said. Ahmad Wali Karzai, the half-brother of President Hamid Karzai heads Kandahar's provincial council.
The explosion and gunfire came hours after NATO forces stationed in the province opened fire on a bus, killing four civilians and injuring 18 others.
The shooting took place on a highway in Kandahar's Zherai district, Zalmai Ayoubi, a spokesman for the provincial governor, said. "Four civilians were killed and 18 others, including women and children, were injured."
The provincial government condemned the attack.
The bus was en route to western province of Nimruz on the Kandahar-Herat highway, where a NATO convoy opened fire on it, the Interior Ministry said in a statement.
Jeff Loftin, a spokesman for the NATO-led International Security Assistance Force (ISAF) in Kabul, confirmed the incident, saying there were some casualties, but could not provide any figures.
He said a joint Afghan and ISAF assessment team was on its way to Kandahar to investigate the incident.
Civilian casualties at the hands of international troops in the country have long been a major source of friction between the Afghan government and more than 120,000 NATO troops currently stationed in Afghanistan.
Afghan and NATO forces are building up an operation in the province, which is regarded as the spiritual home for the Taliban militants in the volatile region.
The offensive is expected to get its bigger push in summer, when thousands of extra US troops are expected to arrive in the region.
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