Security forces clashed with militants at either end of Pakistan’s wild tribal belt Wednesday, killing 19 enemy fighters and wounding dozens more, officials and witnesses said.

Violence is spreading across Pakistan at a moment of particular political upheaval following the resignation of U.S. ally Pervez Musharraf as president and amid a gathering economic storm.

On Tuesday, gunmen fired at the car of a senior U.S. diplomat in the northwestern city of Peshawar and a bomb killed seven at a roadside restaurant near the capital, Islamabad.

In the most dramatic incident Wednesday, the military said between 75 and 100 militants assailed a military fort in the South Waziristan region at about midnight Tuesday.

Troops guarding Tiarza Fort and a checkpoint on a nearby bridge “responded effectively and repulsed the attack,” a military statement said.

It said 11 militants died and between 15-20 were wounded. It made no mention of any casualties among the troops.

South Waziristan lies at the southern end of Pakistan’s tribal belt, a largely ungoverned swath of mountains along the Afghan border from where militants mount attacks on security forces on both sides of the border.

Suspected militant hideouts in the region have been targeted in a stream of suspected U.S. missile attacks, including one that killed a senior al-Qaida commander in July.

Aminullah Wazir, a shopkeeper in Wana, the region’s main town, said security forces imposed a curfew in the area Wednesday. Shops were shut and the streets deserted, he said.

“We heard shelling and gunfire almost all night,” Wazir told The Associated Press by telephone.

A flareup in South Waziristan would leave Pakistan’s military fighting on three fronts.

Troops are already in combat in the Swat valley and in Bajur, the most northerly of the tribal regions and a rumored hideaway for Osama bin Laden and al-Qaida No. 2 Ayman al-Zawahri.

Fazl Rabi, a commander of tribal police in Bajur, said eight militants died when security forces fired on their vehicles in two separate incidents Wednesday. Another 10 militants were wounded, he said.

Rabi provided no further details and spokesmen for the army and for the militants could not immediately be reached for comment.

Officials say hundreds of militants have died in a weeks-old offensive in Bajur, while residents say civilians have also been killed in incidents including mortar strikes on their homes. An estimate 200,000 people have fled to safer areas.

Tensions have also flared in the southern metropolis of Karachi, Pakistan’s economic and financial hub.

A dispute on Tuesday between student followers of two feuding political parties _ one secular, one Islamist _ escalated into a gunbattle that left three people dead on Karachi’s university campus, officials said.

Musharraf resigned Aug. 18 to avoid impeachment charges, triggering a scramble for power that has brought down the coalition of political parties that ended the former coup leader’s nine-year rule.

Lawmakers are expected to elect Asif Ali Zardari, the widower of slain former leader Benazir Bhutto, as Musharraf’s replacement on Sept. 6.

Zardari’s party, which is courting smaller parties to shore up its parliamentary majority, has begun toughening the government’s line against militants.

Still, Pakistanis and the country’s Western backers worry that the political turmoil is hindering efforts to counter rising Islamic extremism and shore up the flagging economy.

On Wednesday, the Karachi stock exchange’s benchmark 100-share index fell another 3 percent. The index has plummeted by more than 40 percent since April and stands at its lowest level in more than two years.

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Associated Press writers Ishtiaq Mehsud in Dera, and Ismail Khan and Ashraf Khan in Karachi contributed to this report.