ISLAMABAD — At least 10 police officers have been killed in an attack on a police station in northwest Pakistan.

Violence has escalated ahead of the country's general elections this week.

Militants launched the attack at about 03:00 local time Monday (22:00 GMT Sunday), first with sniper fire, followed by grenades, according to police in the Draban region in Khyber Pakhtunkhwa province.

The exchange of fire lasted over two and a half hours, injuring nine others.

It is not yet clear who carried out the attack, but the area has seen strikes on government and security targets as well as civilians by the Pakistan Taliban, Islamic State and other militant groups for years.

Last Wednesday, a candidate for the national assembly was shot dead in another part of Khyber Pakhtunkhwa.

Last week in Balochistan, a province in Pakistan's south-west, a political leader was also shot and killed in his party's election office and a bomb attack following a political rally killed at least four people. The Islamic State claimed responsibility for that attack.

The military also killed 24 militants in an anti-terror operation in Balochistan last week.

The Election Commission of Pakistan has categorized half of the country's 90,675 polling stations as either "sensitive", meaning there is a risk of violence, or "most sensitive", indicating a higher risk. The classifications are based on the region's security situation and history of electoral violence. — BBC