A series of explosions rocked southern Afghanistan's volatile Kandahar province on Saturday, killing at least 35 people and wounding 47 others, local officials said.

Provincial Gov. Toryalai Wesa confirmed the blasts hit four locations.

One of the explosions struck near the police headquarters in Kandahar, said Wesa's spokesman, Zalmai Ayoubi. Another blast struck near the province's prison and caused the collapse of some residences.

An unknown number of people are believed to be dead or trapped in the rubble, Ayoubi said.

The casualties include security forces and civilians, he said, adding that both the death toll and the injuries are expected to increase.

Afghan police said two of the four attacks were suicide bombings, while the other two are believed to have been mortar strikes.

Coalition forces in Kabul said the International Security Assistance Force in Kandahar was not targeted.

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Last week, the top U.S. general in Afghanistan vowed that coalition forces "are absolutely going to secure Kandahar," as security efforts expand in the country's south.

"We already are doing a lot of security operations in Kandahar, but it's our intent -- under President [Hamid] Karzai -- to make an even greater effort there," Gen. Stanley McChrystal told reporters Tuesday.

McChrystal indicated a military operation could begin in the province as early as this summer, but McChrystal and Mark Sedwill, the NATO senior civilian representative to the country, cautioned that much political groundwork lay ahead for NATO-led coalition troops before an offensive can begin.

The push to secure Kandahar from what McChrystal calls a "menacing Taliban presence" is part of a larger counterinsurgency effort in the country's south. The effort started last month in Marjah in southern Helmand province.