Afghanistan's Independent Election Commission says preliminary results from the June 14 second round presidential ballot show Ashraf Ghani with 56.44 percent of the vote compared to 43.56 percent for Abdullah Abdullah.
The commission chairman, Ahmad Yousuf Nouristani, on July 7 stressed that the results are preliminary and could change after taking into consideration allegations of fraud or a review of votes that could later be invalidated.
Election officials said turnout was over 8 million, a figure far higher than expected, and which is likely to trigger further allegations of fraud.
Both Ghani, a former finance minister, and Abdullah, a former foreign minister, have accused each other of trying to manipulate the results.
Speaking to RFE/RL's Radio Free Afghanistan shortly after the preliminary results were announced, Fazel Rahman Orya, a spokesman for Abdullah's electoral team, said the Independent Election Commission had "no legitimacy" and that they considered the results "illegal" and "illegitimate."
Abdullah has previously said he will not accept any results until an investigation into all allegations of fraud is completed.
Noman Shinwary, a spokesman for Ghani's electoral team, urged Abdullah's team to join in the process of checking complaints, which he said had been filed by both sides.
Commission chairman Nouristani admitted there had been "technical mistakes" and "shortcomings" in the election process, including some incidents of fraud and violations.
The election commission, however, asked both candidates to "calm down."
Candidates have 48 hours to file formal complaints.
A July 22 deadline has been set to announce the final results.
Representatives of the two rival candidates met ahead of the release of the preliminary results on June 7 to discuss how to defuse tensions over the disputed vote count.
The hotly contested outcome of the election has sparked concerns about a wider split along ethnic lines in Afghanistan.
Ghani attracts support from Pashtuns in the south and east, while Abdullah's loyalists are Tajiks in the north -- echoing the ethnic divisions of the civil war in the 1990s.
The international community had pressed for a smooth transition of power in Afghanistan ahead of the planned withdrawal of international forces by the end of 2014.
With reporting by Reuters, AP, AFP, and dpa