MOSCOW, November 10 (RIA Novosti) - At least 21 people were killed on Tuesday in a car bomb explosion in the northwest Pakistani city of Charsadda, Al Jazeera reported.

The bomb went off on a road intersection near a busy market, and destroyed several shops and cars. The news network said at least 20 other people were injured, and that the death toll is expected to rise.

The attack, believed to have been carried out by militants in retaliation against anti-terrorist operations on the Afghan border, is the third to hit northwest Pakistan in three days. No groups have claimed responsibility for today's blast.

At least 11 people, including a local mayor, were killed and 36 others injured in a suicide bomb attack on the outskirts of Peshawar on Sunday. On Monday, a terrorist in a rickshaw blew himself up near a group of police officers in the city, killing three.

The area separating Pakistan and Afghanistan has been a stronghold for Taliban radicals who fled Afghanistan after the U.S.-led invasion toppled the Taliban regime there in 2001, as well as for Al-Qaeda fighters.