Gunmen armed with rocket-propelled grenades ambushed a police convoy in eastern Punjab province on Thursday, killing at least 11 officers and wounding seven others, authorities said.
No one immediately claimed responsibility for the attack in the Rahim Yar Khan district. The officers were ambushed while patrolling a deserted area in search of robbers who operate in the region.
Punjabi police said the gunmen were likely robbers. The victims were taken to a nearby hospital.
Pakistan has witnessed a surge in violence and attacks in recent years, but such a high number of police casualties in a single attack is rare.
Security forces often carry out operations against bandits in Punjab and in the southern Sindh province, where criminals hide in rural, forested areas and where they have killed several police officers in attacks over the past months.
Thursday's attack was in the district of Rahim Yar Khan's area of Kacha, known for robbers' hideouts along the Indus River, where hundreds of heavily armed bandits evade police.
Police said dozens of bandits launched the attack after one of the police vehicles had apparently broken down while passing through accumulated rainwater along farm fields. Pakistan has been lashed by monsoon rains since July.
Authorities swiftly condemned the Kacha attack, one of the deadliest on police in recent years. President Asif Ali Zardari, Prime Minister Shehbaz Sharif and Interior Minister Mohsin Naqvi released statements denouncing the violence, expressing sorrow and describing the slain officers as martyrs.
Police were ordered to take immediate action against the attackers, and Sharif demanded the best medical care for the wounded officers.
Earlier on Thursday, gunmen opened fire on a school van in Punjab, killing two children and wounding six other people, police said. No one claimed responsibility for that attack.
