At least seven have been killed and more than 80 injured in a suspected bombing inside a religious school in Peshawar, Pakistan, hospital officials said. 

The explosion ripped through the busy madrassa in Peshawar's Dir Colony on Tuesday morning. The victims are believed to include two teachers and many children, including four under the age of 13, who were studying inside the school at the time.

Police said they were still investigating the cause of the blast, but the blast is believed to have been a deliberate act. No group has yet claimed responsibility, however. 

"The blast took place in a madrassa where unknown people had planted explosives in a plastic bag," an officer said.   

Rescue teams are at the scene helping victims, while the tallies of those dead and injured continued to rise on Tuesday morning.

Most of the injured were being taken to the city’s Lady Reading Hospital, Pakistan’s Geo News reported, with many of them suffering burn wounds and in a critical condition.

Pakistan’s Prime Minister Imran Khan tweeted his condolences to the families of victims, saying: “I want to assure my nation, we will ensure the terrorists responsible for this cowardly barbaric attack are brought to justice asap.”  

Later on Tuesday the health minister of Khyber Pakhtunkhwa state, Taimur Saleem Jhagra, visited the site of the blast. He told reporters the focus of the government was on providing the injured with the best possible treatment.

In another incident on Sunday, four people were killed in the explosion of an improvised device in Quetta, the capital of Pakistan’s southwestern state of Balochistan. On 21 October, another powerful explosion was reported in Karachi, the biggest city in Pakistan, where at least five people were killed and 20 were injured.

Last month, also in Khyber Pakhtunkhwa state, an explosion occurred in a market next to the Kabul River in Akbarpura where five people were killed and two were injured. 

In 2014, militants from Tehreek-e-Taliban opened fire at a military school in Peshawar and killed over 150 people, including many children.