KABUL — Defying threats by the Taliban, Afghans turned up at polling stations across the country to vote Saturday in the country’s landmark presidential election, which appeared to be unfolding relatively smoothly despite a string of deadly attacks and allegations of fraud.

The day began somewhat ominously in Kabul as a handful of rockets detonated without causing significant damage shortly before polling stations opened and a slight tremor shook the earth as voters began lining up to cast ballots.

“I’m enthusiastic,” Mohamed Anwar, 61, said as he left a polling station in Kabul Saturday morning, his finger stained by indelible ink. “Most people are eager to vote.”

The contest between former foreign minister Abdullah Abdullah and former finance minister Ashraf Ghani has the potential to mark the first peaceful handover of power in Afghanistan’s history if it is not marred by a disputed result or widespread violence.

A credible election would go a long way to enable the United States to wind up its combat mission here by the end of the year and keep a residual force – as well as sustained financial aid – for years to come.

In Paktia Province in eastern Afghanistan, insurgents began firing rockets Friday night in an apparent attempt to intimidate voters, said Gen. Mohammad Yaftali, the commander of the army’s 203rd corps.

“They’ve been shooting rockets and mortars since last night, trying to create fear so people don’t vote,” he said.

Gen. Dawlat Waziri, the commander of the Afghan Army’s 201 Corps, said 16 people had been killed in clashes on election day in the seven provinces his unit oversees. Most were soldiers, he said.

The scope of the violence around the country and its impact on the election could not be ascertained. It has been hard to promptly determine the level of bloodshed during previous Afghan elections because reports from remote parts of the country are often slow to trickle in. Some polling stations in the east were shut down because of fighting, but officials said they could reopen later in the day.

Still, U.S. officials expressed optimism that violence wouldn’t be the dominant theme of the historic day.

“I think security will not be the issue today, but, as you sense it, the potential for fraud,” Maj. Gen. Stephen Townsend, the top U.S. commander in eastern Afghanistan, told a senior Afghan commander.

Observers working for the campaign of Abdullah in Kabul reported instances of fraud at a couple of polling stations. At one voting site, observers and election commission officials got into a shouting match after an election official was reportedly seen telling elderly men whom to vote for.