KABUL, Afghanistan -- Civilian deaths in the past month jumped by one-third over the same period a year ago, the Afghan government said Sunday.

The surge in noncombatant fatalities is considered particularly worrisome in advance of a major Western military offensive in Kandahar province this spring and summer. Typically, intensified fighting between insurgents and foreign forces brings a corresponding spike in civilian casualties.

Afghanistan's Interior Ministry said 173 civilians were killed between March 21 and April 21, the most recent period for which figures were available. That represented a 33 percent increase from the same dates in 2009, ministry spokesman Zemari Bashary told a news conference in Kabul.

Bashary said the deaths, coupled with the injuries of 380 civilians, largely were caused by explosions -- either suicide bombings or roadside bombs. The latest example of that came Sunday, when officials in Paktia province, near the Pakistan border, reported a civilian minibus had hit an improvised explosive device, or IED, wrecking it and killing or maiming most of those aboard.

Conflicting reports of the number of dead and injured could not immediately be resolved, but it appeared at least half a dozen people had been killed and approximately twice as many hurt, with women and children among the casualties.

IEDs almost always are planted by insurgents with the aim of striking military convoys, but civilians travel the same roads, and their rickety cars and buses -- usually packed with passengers -- are far more vulnerable to attack than the armored vehicles used by troops.

Civilian deaths have exacerbated tensions between the government of Afghan President Hamid Karzai and his Western backers. Karzai has repeatedly denounced noncombatant fatalities and urged greater care on the part of foreign troops, even though most such deaths are blamed on insurgents.

U.S. Army Gen. Stanley A. McChrystal, the commander of all Western troops in Afghanistan, has made safeguarding civilian lives a top priority. But military officials acknowledge that noncombatants are often caught in harm's way during upsurges in battlefield activity, such as the fighting earlier this year in Helmand province, where U.S. Marines seized the Taliban stronghold of Marjah.

Military officials describe the planned Kandahar offensive, expected to peak over the summer, as akin to tightening a noose on the city, the spiritual home of the Taliban movement. They say emphasis will be placed on controlling routes in and out of the city, and taking steps to restore people's confidence in the Afghan government.