PARACHINAR, Pakistan — Pakistan's army fought Islamist militants for control of a northwestern district today, killing 18 of them in an escalating campaign against insurgents intent on toppling the U.S.-allied government.

It was the second day of fighting in Shahukhel in Hangu district close to the Afghan border. On Sunday, 12 militants were killed in the same area, officials said.

Like other parts of the lawless frontier zone, Hangu is home to al-Qaida and Taliban insurgents that launch attacks in Pakistan, as well as in Afghanistan.

Pakistan is under pressure to crack down on militants and has won praise from its Western allies for an ongoing, major operation in the South Waziristan border region. But critics say the army should do more against insurgent groups who use the northwest as a safe haven to attack Western troops in Afghanistan.

Hangu is about 93 miles north of South Waziristan.