Former Foreign Minister Abdullah Abdullah won most votes with 44.9%. Former World Bank economist Ashraf Ghani came second with 31.5%.
They are now expected to face a run-off vote on May 28.
Final official results are due to be announced on May 14 after a period for adjudication of complaints.
Full preliminary results were due two days ago.
The delay has fuelled allegations on all sides that ballot boxes were stuffed and the count was rigged, our correspondent says.
Power-sharing scotched
Abdullah Abdullah and Ashraf Ghani could now form a power-sharing deal, or choose to go to a second round.
Before the results were announced, both men promised to fight in a run-off.
“We have not talked or negotiated with anyone about forming a coalition government,” Abdullah Abdullah told reporters on Thursday.
Millions of Afghans defied Taliban threats to take part in the election.
Turnout was double that of the previous presidential election in 2009, despite a number of attacks in the run-up and bad weather on polling day.
Afghanistan’s current President Hamid Karzai was constitutionally barred from standing for a third term.
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