Thousands of anti-government protesters armed with wire cutters and backed by cranes marched on Pakistan’s parliament Thursday, planning to remove barriers blocking them from soldiers guarding the seat of the country’s government. Pakistani television channels showed live footage of the troops taking positions in the so-called “Red Zone,” which also holds the president and prime minister’s ceremonial homes and many diplomatic posts. That set up a possible showdown between hundreds of soldiers and some 30,000 protesters backing opposition candidate Imran Khan and anti-government cleric Tahir-ul-Qadri. Both men have called on by Prime Minister Nawaz Sharif to step down over allegations...