ISLAMABAD, March 15 (Xinhua) -- At least seven persons, including four policemen, were killed and over 20 others injured Wednesday evening as a blast hit a police check post in Pakistan's eastern city of Lahore, the provincial health minister said.

Punjab Health Minister Khawaja Imran Nazir said that the death toll has risen to seven after three of the wounded succumbed to their injuries during treatment.

Hospital officials feared that the death toll might further rise as some of the injured were in critical condition.

Deputy Inspector General of Lahore Police Haider Ashraf said that the blast hit a police check post in Raiwind Town located on the outskirts of Lahore, the provincial capital of Punjab province.

Police and rescue teams rushed to the site and shifted the bodies and the injured to the Sharif City Hospital, Jinnah Hospital and Tehsil Headquarters Hospital in the city.

Nature of the blast is not known yet. However, local media reported that a bomb fixed in a motorcycle exploded with a big bang soon after a police patrolling party reached the check post near a famous religious center.

The Bomb Disposal Squad of police is examining the site to determine the nature of the blast.

Security forces and police have launched a search operation in the area and a security high alert has also been announced in the city. No group has claimed the incident yet.

Chief Minister of Punjab Shahbaz Sharif condemned the attack and asked the authorities concerned to provide the best available medical treatment to the injured.