Militants opened fire on a police vehicle and killed two officers on Thursday in restive northwest Pakistan before fleeing the scene, police said, a sign of increasing violence ahead of a summit of an Asian security grouping in the capital, Islamabad.
Hours later, the military said it killed four militants in North Waziristan, a district in Khyber Pakhtunkhwa province bordering Afghanistan.
The latest attack on police happened in the city of Tank, also in Khyber Pakhtunkhwa, local police official Sher Afzal said.
No group has claimed responsibility, but suspicion is likely to fall on the Pakistani Taliban, known as the Tehreek-e-Taliban Pakistan or TTP, who often target security forces.
The TTP are outlawed in Pakistan. They are separate from but a close ally of the Afghan Taliban who control neighboring Afghanistan.
Pakistan has witnessed a surge in militant violence in recent months.
A suicide bomber dispatched by the Baloch Liberation Army, an outlawed separatist group, struck a convoy carrying Chinese nationals outside an airport in Karachi on Sunday, killing two engineers and wounding another.
The latest violence comes ahead of the summit of the Shanghai Cooperation Organization, which will take place in Islamabad on October 15.
The Asian group was established in 2001 by China and Russia to discuss security concerns in Central Asia. Its other members are Iran, India, Pakistan, Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan.
The killing of the Chinese has drawn condemnation from Pakistan's leaders.
On Thursday, President Asif Ali Zardari visited the Chinese Embassy in Islamabad, where he met with Ambassador Jiang Zaidong to offer condolences. Zardari denounced the attack and promised that those behind it would be punished, a government statement said.
Also on Thursday, Chinese Foreign Ministry spokesperson Mao Ning told a news conference in Beijing that "China will work with Pakistan to protect the safety and security of Chinese personnel, projects and institutions in Pakistan."
But she said she didn't know if the movement of the Chinese nationals was being restricted because of the summit. Security in Islamabad was beefed up, with the authorities deploying troops, shutting schools and closing two restaurants on the road that will take guests from the airport to the summit venue.
Thursday's developments came a day after at least three people were killed in clashes in the northwestern town of Jamrud between police and supporters of a banned organization, the Pashtun Protection Movement, or PTM, which authorities say supports TTP.
The government has also barred PTM from holding rallies in the northwest, allegedly because the demonstrations are against the interests of Pakistan. PTM denies backing the Pakistani Taliban, and tension was growing Thursday after the group vowed to resist the ban on its rallies.
