Tens of thousands of people massed Sunday in the eastern city of Lahore for a rally held by cricket star-turned-politician Imran Khan, a surprising show of force that could energize calls for anti-government protests.

Police and Pakistani media estimated that at least 100,000 people gathered to see Khan, whose anti-American, anti-corruption rhetoric has made him a populist sensation among elite urban youth. The turnout stunned many Pakistani analysts, most of whom view Khan as a one-man show with a following far too narrow to dent Pakistan’s entrenched political landscape. Khan’s party has no seats in parliament.

But public disillusionment with the U.S.-backed civilian government and unpopular President Asif Ali Zardari is high, and political jockeying ahead of national elections in 2013 is well underway.

Khan’s rally capped a weekend of demonstrations that started Friday when the main opposition party of former prime minister Nawaz Sharif drew thousands in Lahore to call for the government’s ouster. That was countered Sunday afternoon in the city of Karachi, where devotees of one party in the ruling coalition thronged streets to display support for the government.

But neither of those rallies was as big or enthusiastic as Khan’s, at which pop stars sang to a dancing, flag-waving crowd from Lahore and beyond. Most immediately, the numbers represent a threat to Sharif’s party, whose stronghold is Punjab province, of which Lahore is the capital.

Khan, like Sharif, is agitating for a widespread protest campaign — what he called a “tsunami” rolling toward the federal capital — and his ability to drum up a massive turnout is likely to worry the government, which aspires to be Pakistan’s first-ever democratically elected administration to complete its term. Speaking to an English-language television network, one ruling party official dismissed the rally as a “musical concert.”

Khan’s speech, unlike the crowd, was viewed as unremarkable. He called for politicians — widely viewed here as corrupt — to declare their assets or face an investigation by a “special cell” set up by his party. He said little about the military, which remains Pakistan’s most powerful force, and which is believed to favor Khan.

Khan’s young party workers vigorously employ social media to spread his message, and participants and observers offered play-by-play accounts of the rally on Twitter.

“Today’s rally shows that the old political configuration is changing. You have to factor in the young, urbanized Pakistan clamoring for good” governance, tweeted Raza Rumi, a prominent commentator.

Khan is a staunch critic of CIA drone strikes in Pakistan’s militant-riddled tribal belt, which have increased in recent weeks. On Sunday, four to six drone-fired missiles slammed into a vehicle in the town of Datta Khel in North Waziristan, a hub for al-Qaeda and Afghan Taliban fighters, according to two Pakistani intelligence officials. At least four militants were killed, but they remained unidentified Sunday evening, the officials said.

Special correspondent Haq Nawaz Khan contributed to this report from Peshawar, Pakistan.