Media playback is unsupported on your device Media caption The electoral complaints commission will go through "a lot of complaints to do with ballot stuffing, allegations of fraud", reports Bilal Sarwary

The Afghan presidential election will go to a second round, after no candidate reached the 50% needed for an outright win, preliminary results show.

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 28 May.

Final official results are due to be announced on 14 May after a period for adjudication of complaints.

Analysis It has been clear since the first results emerged that there were only two candidates who stood a chance of winning. Abdullah Abdullah and Ashraf Ghani were far ahead of the rest. Both have insisted since then that the Afghan people should decide the outcome: there should be no backroom deal to avoid a second round. But the electoral maths are increasingly with Dr Abdullah, and he is now considering his options. He has extended his lead to 13 points ahead of Dr Ghani, and is expecting to pick up most of the voters who backed the next strongest candidates - Zalmai Rassul and Abdul Rasul Sayyaf. Dr Abdullah has been publicly generous about the sitting president, Hamid Karzai, although he lost a bitterly fought election in 2009. Intensive discussions are now going on behind the scenes, and a second round might yet be avoided. Security forces, fearing worse violence if there is polling at the height of the summer, would be very relieved.

The BBC's David Loyn in Kabul says there are increasing claims of fraud.

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

Mr Abdullah and Mr 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," Mr 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.

Current President Hamid Karzai was constitutionally barred from standing for a third term.

The next president will face several challenging issues, including the expected withdrawal of foreign combat troops later this year and attacks by the Taliban.