Separately in the east, police and U.S.-led coalition forces attacked suspected Taliban insurgents crossing from Pakistan into Afghanistan, killing 10 militants and wounding 15, the provincial governor said Sunday.
The security firm, U.S. Protection and Investigations, said that a suicide bomber riding a motorcycle blew himself up near a convoy, killing two employees and wounding another.
Mohammad Asif Khan, a police officer 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 and their driver were killed, Khan said. The differing death tolls could not immediately be reconciled.
The attack in Kandahar comes a day after a suicide bomber blew himself up next to several Afghan border policemen in eastern Khost province, leaving at least seven officers and one civilian dead.
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.
On Saturday night, police and coalition forces launched an operation against a large number of suspected Taliban fighters who were seen entering Paktika province's Barman district from Pakistan, said Paktika Gov. Mohammad Akram Akhpelwak.
Ten militants were killed, including one Arab, and 15 were wounded, Akhpelwak said. One Pakistani national was arrested and the insurgents left several AK-47s and rocket propelled grenades behind, he said, adding that police and coalition forces suffered no casualties.
Afghan and western officials have stepped up pressure on Pakistan to crack down on militants who organize and train in Pakistan's tribal areas, and then cross the border to launch attacks and wreak havoc in Afghanistan.
Fighting between militants and foreign and Afghan forces appeared to be intensifying after the usual winter lull, with at least six Taliban killed in a clash in Helmand province on Saturday, a statement from the U.S.-led coalition 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.