Seven police officers were killed while protecting health workers who were vaccinating children against polio in the Pakistani city of Karachi, authorities said.

Gunmen on motorcycles opened fire on the officers as they stood guard outside a house in the port city, local police adviser Ahmed Chinoy said.

Speaking at a news conference, Ad Khawaja, the police chief for Sindh Province, said authorities had identified the group responsible for the twin attacks.

Shell casings found at the two crime scenes matched those from previous attacks.

Pakistani Prime Minister Muhammad Nawaz Sharif released a statement condemning the attacks.

“(The officers) sacrificed their today for securing the future of our coming generations,” he said.

“The entire nation will fight against these cowards with unity and unshattered resolve.”

Meanwhile, Ehsanullah Ehsan, a spokesman for a splinter group of the Pakistani Taliban, Tehreek-e-Taliban Pakistan Jamaatul Ahrar (TTP-JA), claimed responsibility for the attack.

“Our attacks against security agencies and officials will continue and the Karachi attack was a continuation of this struggle to implement Islamic government in Pakistan,” he said in a statement.

TTP-JA also claimed responsibility for an attack on a Lahore park last month.

Polio workers in Pakistan have been targeted by Islamist militants before.

In January, 14 people, including 13 police officers and a paramilitary trooper were killed and 25 others injured when a suicide bomber attacked a government-run polio drive in Quetta.

Militants have targeted anti-polio campaigns in Pakistan for decades in an effort to beat back government influence.

Pakistan remains one of two countries, alongside Afghanistan, where polio is endemic, according to the World Health Organization.

In 2011, U.S. intelligence officials used a vaccination program to help in their hunt for Osama bin Laden.
Under cover of the program, the CIA sought to collect DNA samples from relatives of the al Qaeda leader to verify his presence in a compound in Abbottabad, Pakistan.

The revelation of the CIA scheme reinforced the militants’ existing fear of vaccinations.