"I'm confident this election won't lead to the formation of a new government," Suthep told supporters late on Sunday.
Giving provisional data on Monday, the Election Commission said 20.4 million people cast their vote on Sunday, just under 46 percent of the 44.6 million eligible voters in 68 of 77 provinces. In the other nine provinces, no voting was possible.
Voting was disrupted in 18 percent of constituencies, 67 out of 375, the commission said, revising data given Sunday.
It could be weeks before seats in the constituencies that saw disruption are filled and parliament can be convened, so Yingluck will remain a caretaker premier with no policy authority, unable to approve any new government spending.
(Read more: Has Thailand's government survived the gauntlet?)
"Having gone through more than two months of protests, the election will strengthen Yingluck's position, but her troubles are not over yet," said Kan Yuanyong, director of the Siam Intelligence Unit think tank.
"We'll see a continuation of the conflict, the standoff remains and the likelihood of more violence could increase."
The turmoil is taking an economic toll with tourism in particular being hit.
The protesters say former telecoms tycoon Thaksin has subverted a fragile democracy with populist politics such as subsidies, cheap loans and healthcare to woo the poor and guarantee victory for his parties in every election since 2001.
Thaksin's critics also accuse him of disrespecting Thailand's revered monarchy, which he denies.
Thaksin has lived abroad since 2008 to avoid a jail term for a graft conviction he says was politically motivated. Critics say Yingluck is merely a stand-in for him.
(Read more: We don't mind if we lose 'fair elections': Abhisit)
Thaksin's supporters accuse the military and the establishment, including the judiciary, of colluding over the years to oust his governments.
The military, which has staged numerous coups since Thailand became a constitutional monarchy in 1932, overthrew Thaksin in 2006 but has stayed aloof this time.
The State Department's Psaki said the United States "certainly" did not want to see a coup in Thailand.
"We are speaking directly to all elements of Thai society to make clear the importance of using democratic and constitutional means to resolve political differences," she said.