Nov. 13 (Bloomberg) -- An explosion hit Pakistan’s northwestern city of Peshawar early today, killing 18 people and damaging the office of the country’s intelligence agency, the ambulance service said.

At least 100 people were injured, Zulfiqar Khan of the Edhi Foundation, which runs the country’s largest ambulance service, said by telephone. The office of the Inter-Services Intelligence agency in North West Frontier Province was damaged by the blast, he said.

Two separate bombings in Peshawar, the provincial capital, killed at least 17 people on Nov. 8 and 9. A suicide bomber blew himself up in a car at a market in the town of Charsadda in the northwest of the country three days ago.

Militants have mounted a campaign of suicide bombings and attacks after Pakistan’s army last month began its largest offensive to clear pro-Taliban fighters from South Waziristan, a tribal region bordering Afghanistan.

More than 300 people have been killed since mid-October in attacks in towns and cities, including the capital, Islamabad.

The militants are mounting a “desperate” guerrilla war after suffering defeats in South Waziristan, Prime Minister Yousuf Raza Gilani said Nov. 10.

Attacks in recent weeks have included the army headquarters in Rawalpindi last month, police complexes in the eastern city of Lahore and twin suicide bombings at the International Islamic University in Islamabad.

The army operation in South Waziristan is targeting the Tehreek-e-Taliban, the group Pakistan blames for 80 percent of terrorist attacks on its territory.

To contact the reporter on this story: Farhan Sharif in Karachi at fsharif2@bloomberg.net.

Last Updated: November 13, 2009 06:48 EST