KABUL: A bomb tore through a car in Afghanistan Wednesday and killed seven civilians while authorities reported that scores of other people, mostly militants, were killed in other violence.

A tide of unrest has reached record levels in Afghanistan nearly eight years after the Taliban regime was ousted, prompting the United States to rethink its strategy amid fears the bloodshed could overshadow August elections.

A roadside bomb of the sort used by Taliban against security forces struck a civilian estate car in the turbulent southern province of Helmand, the interior ministry said in a statement.

"Today seven civilian countrymen were martyred when a mine planted by the enemies blew up their vehicle," it said, adding four others were wounded.

The province has seen heavy military operations in recent weeks as security forces try to clear out insurgent hotspots ahead of August 20 presidential and provincial council elections.

Afghan soldiers have killed 48 militants in two operations in Helmand and adjoining Uruzgan this week aimed at clearing Taliban strongholds, Afghan officials announced Wednesday.

Local troops backed by NATO-led international forces stormed a militant stronghold in Uruzgan on Tuesday, killing 23 insurgents, Afghan army General Sher Mohammad Zazai told AFP.

Fighter jets from the NATO force took part in the battle, close to the provincial capital of Tirin Kot and near the Pakistan border, he added.

The Afghan defence ministry reported separately that troops had killed 25 "terrorists" in a four-day clean-up operation that ended on Tuesday in the southern province of Helmand.

NATO's International Security Assistance Force said separately its troops, working with Afghans, had killed 25 militants in the neighbouring province of Kandahar on Tuesday and Wednesday.

It was not clear if they were referring to the same incident reported by the defence ministry.

"Approximately 25 insurgents were killed in the engagement with one being captured and currently being detained for questioning," it said in a statement.

In other violence, two Afghan intelligence officers were killed late Tuesday in the southern province of Zabul, provincial governor Mohammad Ashraf Nasery said.

Police in the same province killed four Taliban who had attacked a convoy on the same day, he said.

The new attacks came as US national security adviser James Jones visited Afghanistan as part of a tour to assess implementation of a new US strategy against the Taliban that promises more troops, money and development.

Jones started his trip in Kabul on Tuesday where he met President Hamid Karzai and the top US commander, General Stanley McChrystal, who took over just over a week ago. On Wednesday he was in Helmand.

In Kabul he stressed US commitment to securing the August 20 presidential elections, a milestone in international efforts to bring democracy to Afghanistan after the 1996-2001 Taliban regime was toppled in a US-backed invasion.

The Taliban insurgency has grown steadily in recent years, and picked up again in recent weeks, raising fears for the security of the elections.

There are about 90,000 foreign troops -- mostly from the United States -- stationed in Afghanistan to battle the Taliban and help train Afghan forces.

The main producer of Afghanistan's illegal opium, Helmand sees some of the worst of the insurgency, with a handful of districts said to be under insurgent control.