A homicide car bomber targeted a private U.S. security firm Sunday in southern Afghanistan, killing up to four Afghans working for the company and wounding another, police said.

The security firm, U.S. Protection and Investigations, said that a homicide bomber riding a motorcycle blew himself up near a convoy, killing two employees and wounding another.

Mohammad Asif Khan, a policeman in Kandahar province's Spin Boldak district, said the attack occurred on a main highway in the district, where the company was providing security for road construction projects. Three security guards were killed, along with their driver, Khan said. The differing death tolls could not immediately be reconciled.

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On Saturday, a homicide bomber blew himself up next to several Afghan border policemen in eastern Khost province, leaving at least seven officers and one civilian dead, while six suspected Taliban were killed in the south, officials said.

The explosion happened as the bomber tried to enter the border police base in Khost, said Gen. Qasim Kheil, a border police commander. Six officers also were wounded in the blast, he said.

The attack happened as fighting between militants and foreign and Afghan forces appears to be intensifying after the usual winter lull.

In the volatile south, U.S.-led coalition and Afghan troops clashed with suspected Taliban in Helmand province also on Saturday, a coalition statement said. Troops called in an airstrike on an observation site used by the Taliban, leaving six militants dead, the statement said.

Earlier, officials said U.S.-led troops and aircraft pounded Taliban militants in southern Afghanistan, killing more than 70 in two separate clashes on Thursday, as NATO-led troops pressed on with their largest-ever anti-Taliban offensive in Afghanistan's insurgent-haunted south.

More than 5,000 NATO and Afghan troops are engaged in Operation Achilles, launched last month to flush militants entrenched in the northern tip of the opium-producing province.

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