At least 59 people, mostly policemen, were killed and 157 others injured after a suicide bomber blew himself up in a mosque in Peshawar's Police Lines during 'Zuhr' prayers (around noon) on Monday, reports said.

The outlawed Tehreek-e-Taliban Pakistan (TTP), which late last year called off its ceasefire with the government and carried out a series of attacks, including in a Peshawar police station in December, has taken responsibility for the blast.

According to security officials, the suicide attacker was present in the front row during the Zuhr prayers when he detonated the explosives, Geo News reported.

Imam Sahibzada Noor ul Amin was also killed in the blast, police said.

The blast also brought down the mosque's roof, trapping many under the debris, and rescue operations were on to extricate them.

Local media quoted an eyewitness, who was going to the mosque when the explosion took place, as saying that it was "a powerful explosion" and "there was smoke everywhere".

"There were at least 120 people in the mosque when the incident took place. It was a suicide blast because the bomber was inside the mosque's inner courtyard. The Zuhr prayer had just started when it happened. There were mostly policemen among the injured," the eyewitness said, adding that he later saw that the mosque's roof had collapsed.

Prime Minister Shehbaz Sharif, accompanied by top ministers including Defence Minister Khwaja Asif and Interior Minister Rana Sanaullah, has reached Peshawar where he was briefed by officials and visited the injured in hospitals. Chief of Army Staff, General Syed Asim Munir, has also reached the provincial capital and accompanied the Prime Minister.

Asif told Geo News that the roof fell due to the intensity of the blast, and the city's hospitals have been overwhelmed.

He said that the police have been targeted, emphasizing that the machinery that controlled terrorism before needs to be activated again.

Khyber Pakhtunkhwa's Inspector General of Police Moazzam Jah Ansari said that "investigations are underway" about how the terrorist entered the highly-secure area, where the headquarters of the Peshawar Police, the Counter-Terrorism Department, the Frontier Reserve Police, the Elite Force, and Telecommunications Department are also located.

He apprehended that "there are family quarters inside the Police Lines and the attacker could be already living in the area", Geo News reported.

There is also speculation on how the suicide bomber managed to reach the mosque.

Civil Secretariat Association Peshawar Tassavur Iqbal, who regularly prays at the mosque, said that the Police Lines area's security is always high and no one can enter without showing their identity and a body search, Geo News reported.

A local journalist noted that the Police Lines are located in Peshawar Cantt's most sensitive area where a large number of security personnel are present round the clock, and to reach there, one has to cross at least two police checkposts.

Meanwhile, the injured were taken to the Lady Reading Hospital and it appealed to citizens to donate blood for the victims. Khyber Pakhtunkhwa's caretaker Chief Minister Muhammad Azam Khan imposed a medical emergency in all hospitals of Peshawar and asked rescue organizations to speed up relief activities.

Lady Reading Hospital spokesman Muhammad Asim said that 157 injured people were brought there after the blast.

"Bodies of 44 people were also transferred to the hospital. At the moment, around 65 injured are getting treatment. Some of the injured are critical, while the condition of most is satisfactory," he said, adding that most people among the injured and dead included police officers.

The attack was condemned by top leaders of the country.

President Dr. Arif Alvi deemed the attack "heinous and cowardly", and asserted that the perpetrators would be found and punished.

PM Shehbaz Sharif said that the blast inside a mosque proves that those involved in the attack have "nothing to do with Islam".

"These terrorists are trying to instill fear by targeting those who perform the duty of defending Pakistan," he said, assuring the people that the coalition government will take strict action against those involved.

Foreign Minister Bilawal Bhutto-Zardari, condemning the incident, said that strict action will be taken against the terrorists, their backers, and facilitators.

PTI Chairman Imran Khan also took to Twitter to condemn the suicide attack.

"My prayers and condolences go to the victims' families. It is imperative we improve our intelligence gathering and properly equip our police forces to combat the growing threat of terrorism," said Khan.

Former President and Pakistan Peoples Party (PPP) Co-chairperson Asif Ali Zardari condemned the incident, saying that the terrorists being active in Khyber Pakhtunkhwa is "extremely dangerous".

Former Chief Minister Mahmood Khan strongly condemned the incident, saying that the blast is very "heartbreaking".

Meanwhile, in wake of the blast, the Inspector General of Islamabad Dr. Akbar Nasir Khan issued orders to put security on high alert in the federal capital. (KB/IANS)