Image copyright Reuters Image caption Final results from October's parliamentary elections have not yet been declared

Next year's presidential election in Afghanistan has been postponed by three months, election authority sources say.

It was initially due in April. A new date in mid-July or early August is to be announced on Thursday.

Many potential candidates had been unable to meet registration requirements and extreme weather meant their teams could not organise for a spring date, the sources told the BBC.

It comes days after reports that the US was to withdraw thousands of troops.

About 7,000 troops - roughly half the remaining US military presence in the country - could go home within months, the US media reports said.

On Monday 43 people died in a suicide and gun attack on the Afghan ministry of public works in Kabul, officials said.

Meanwhile Iran has held talks with the Afghan Taliban, a senior Iranian security official said.

The decision to postpone the presidential vote also comes after a series of problems affected parliamentary elections in October, which was disrupted by the Taliban and Islamic State group.

Violence affected campaigning and the polls themselves, with 10 candidates killed and deadly blasts at polling stations, nearly a third of which were closed because of security concerns.

Image copyright Reuters Image caption There were widespread problems with biometric identification devices used in October

The vote in Ghazni province has not yet taken place because of insecurity and will now happen at the same time as the presidential election.

Voting in Kandahar province was delayed for a week after its police chief there was assassinated.

There were also problems with a biometric verification system as well as delays at many polling stations because staff arrived late.

Final results from other major provinces such as Kabul, Herat and Mazar-e-Sharif have not yet been declared. The new parliament is due to begin sitting in March.

Past elections in the country have also been marred by corruption, fraud, and voter intimidation.

The previous presidential election - which saw Ashraf Ghani take power - was only resolved after a power-sharing agreement was negotiated by the US with Mr Ghani's main rival, Abdullah Abdullah, who was given the position of chief executive.