Kandahar, Afghanistan ? An explosion ripped through a bus and heavy fighting erupted between government soldiers and Taliban remnants Wednesday, one of the bloodiest days in Afghanistan since U.S.-led forces ousted the hard-line Islamic regime.

The bus bombing killed 15 civilians — six of them children; the death toll for Wednesday — including two explosions and gunbattles in two provinces — was 58.

The deaths were part of a trend of stepped-up attacks and killings that are increasing the pressure on the fragile Afghan government and creating an atmosphere of constant fear in the country.

In addition to 21 fighters killed in Khost province near the Pakistani border, two students died making a homemade bomb and 20 men were killed in a feud in southern Uruzgan province between rival commanders both loyal to President Hamid Karzai’s government.

Officials were quick to blame al-Qaida insurgents and Taliban loyalists for the bus explosion in Nadh Ali district, about 20 miles southeast of the Helmand provincial capital Lashkargah.

“The Taliban do not want peace in the country. They don’t want a government to be established. That’s why they want to create instability and make the people of Afghanistan afraid,” Ghulam Mahauddin, a district administrator, told The Associated Press by telephone.

He also speculated that the blast was an accident: Someone may have been transporting explosives to carry out a terror attack in Lashkargah when the bomb went off prematurely.

“We’re investigating all possibilities,” Mahauddin said. “Right now, we don’t think it was a suicide bomber or that it was a remote-controlled device. It seems that someone placed the bomb in the bus. Whoever did this is an enemy of Afghanistan.”

Five civilians including the driver were wounded in the blast, three of them seriously.

The explosion was one of the deadliest incidents since a car bomb killed 30 people and wounded 150 others in the capital, Kabul, on Sept. 5, 2002.

Meanwhile, fighting between Afghan troops and suspected Taliban militants broke out late Tuesday and continued early Wednesday in Shinki, a village in eastern Khost province about four miles from the Pakistan frontier, said Ghafar Khan, who commands a border police battalion in area.

Khan said insurgents attacked three times Tuesday night to test their opponents’ strength. A group of 80 attackers launched an all-out assault just before dawn Wednesday.

When it was over, the bloodied bodies of 16 insurgents were found on the battlefield. Khan said five Afghan soldiers were killed before the attackers retreated across the border into Pakistan.

Afghan troops captured two Arabs who had been wounded in the fight, Khan said. Their nationalities were not known.