Afghanistan’s incumbent president, Ashraf Ghani, won a slim majority of votes in September’s election, according to preliminary results, after a poll that plunged the country into political crisis and was marred by allegations of fraud.

The Independent Election Commission (IEC) said the total turnout in the presidential election was more than 1.8 million with Ghani securing 50.64% – enough to win in the first round of voting – beating his main challenger, Abdullah Abdullah, who shares power with Ghani in a unity government.

Abdullah’s office said in a statement that he did not accept the preliminary results published on Sunday and that the commission had failed to tackle election fraud.

In a televised speech on Sunday, Ghani welcomed the result and said the country was on the right path towards prosperity and development.

“With the announcement, we are moving now from darkness to light and from uncertainty to a bright future,” Ghani told a jubilant crowd gathered at the presidential palace in Kabul.

The head of the IEC, Hawa Alam Nuristani, told a news conference in Kabul earlier that the outcome could change after final results and was still subject to a review by the election complaints’ commission.

If a review showed Ghani’s vote falling below 50% and no other candidate with a majority, a second round of voting would be held, she said.

According to the tally released by the IEC on Sunday, the total turnout was 1,824,401 with Ghani winning 923,868 votes. Abdullah finished second with 39.5% and 720,099 votes.

The US, Afghanistan’s biggest donor, reacted cautiously to the result.

“It is important for Afghans to remember: these results are preliminary. Many steps remain before final election results are certified, to ensure the Afghan people have confidence in the results,” John Bass, the ambassador to Afghanistan, said in a post on Twitter.

With 9.7 million registered voters, according to the IEC, turnout was at a record low for an Afghan presidential election. Last month, the IEC began recounting thousands of votes due to what it described as discrepancies in its system. Abdullah’s side objected to the recount and called it an attempt to add more votes in favour of Ghani. The IEC dismissed those allegations.

In protest, Abdullah’s supporters blocked IEC offices in seven northern provinces to prevent the recount, creating delays in the results’ announcement. Last week, Abdullah allowed the recount but warned that he would not accept a tainted result.

“The result that stands is based on fraud and without considering our legitimate demands, will never be accepted,” Abdullah Abdullah’s office said in statement on Sunday.

The situation echoes 2014, when both Ghani and Abdullah alleged massive fraud by the other, forcing the US to broker an awkward power-sharing arrangement that made Ghani president and Abdullah his chief executive.

Aides close to Ghani, a western-educated former World Bank official, said the incumbent was not ready for another power-sharing deal with Abdullah, a former medical doctor and three-time contender for the presidency.

Without a unifying leader accepted by all sides, Afghanistan could split further along tribal and ethnic lines.

The election result also comes at a critical time for Afghanistan as the US is showing more interest in negotiating a peace settlement with the Taliban to end a war that has dragged on for more than 18 years.

Eighty-five civilians were killed and more than 370 wounded in militant attacks and violence on the day of the election, the United Nations said last month, and the country plunged into chaos with both Ghani’s and Abdullah’s camps claiming victory before ballots had been tallied.

Election result announcements in Afghanistan are typically followed by violent protests from supporters of losing candidates.