At least 23 people were killed and 20 injured Monday in a head-on collision between two passenger buses in Bangladesh.The smash-up took place on the Banparha-Hatikumrul highway in Natore district, bdnews24.com reported. Natore Superintendent of Police Basudeb Banik said the number of people killed could further rise.Police have begun a probe into the cause of the accident.Traffic on the highway has been interrupted due to the crash.