Voting is drawing to a close in Afghanistan's second presidential election since the fall of the Taliban.
Militants threatened to disrupt the polls, in which President Hamid Karzai is running for a second term.
Reports suggest turnout has been patchy, with fewer voting in the south, where militant influence is greater.
There is a huge military presence to try to deter attacks - but there have been violent incidents including a deadly gun battle in Kabul.
There were other fatal incidents, as well as small rocket attacks reported around the country.
The election follows a lively campaign period in which dozens of candidates vied for the presidency - but it was marred by violent attacks and frequent complaints of pre-election corruption and fraud.
Some 300,000 Afghan and international troops are on patrol trying to prevent attacks.
Violent incidents around the country include:
- Taliban militants set fire to a bus on the Kandahar-Kabul highway in Ghazni, after offloading passengers and the driver, reportedly as punishment for violating a Taliban ban on using the road
- A woman was reportedly killed by a rocket in Kandahar
- A woman died and three children were injured when rockets hit a house in southern Khost province
- Also in Khost, a civilian car hit a roadside bomb, killing one person and injuring three
- Two suicide bombers on a motorbike in Gardez, Paktia province, were killed before hitting their target, police said
- In northern Baghlan province, a district police chief was killed when Taliban militants attacked a police post
- In Kabul, the bodies of two alleged militants were recovered after a gun battle with police in a residential district - police said they were suicide bombers but it is unclear whether they blew themselves up or were shot dead.
Polling stations opened at 0700 (0230 GMT) for voting in what is Afghanistan's second direct presidential election since 2001, but the first organised primarily by Afghans themselves.
Voters are also electing members to provincial councils.
The vast majority of the country's 6,969 polling stations had been able to open despite the security threat, the UN said.
Speaking on state TV, the director of Afghanistan's Independent Election Commission, Azizullah Loudin, claimed turnout had been "high".
Apart from the earlier gun battle in Kabul, the city was mainly reported to be quiet, with a brisk turnout in some polling stations while there was little activity in others.
Despite repeated blasts being heard in Lashkar Gah, the provincial capital of militant stronghold Helmand province, lots of voters were coming out, though in next-door Kandahar turnout appeared to be low.
And in Jalalabad, eastern Nangarhar province, some districts reported no voters at all.
The BBC's Martin Patience points out that three-quarters of Afghans live in the country's 30,000 rural villages - so it is turnout in the countryside which is key.
A voter in Kabul said she hoped the election would bring peace and security to Afghanistan.
"We want the next president to stop the killing of innocent people and to find jobs for the people, and bring peace."
But other would-be voters said they feared for their safety, while yet others said they had little faith in Afghan democracy.
"Unfortunately, democracy has been exported to Afghanistan, it hasn't grown up from the bottom to the top," said one.
"We are hoping that the United Nations and the rest of the world's powers should pay attention to this to help the Afghan people to grow democracy from the inside."
Across the country, some 17 million Afghans are eligible to vote until polling stations close at 1600.
There were widespread concerns about corruption in the run up to the poll, with reports of voting cards being openly sold and of candidates offering large bribes.
The government was criticised for imposing a ban on election-day coverage of violence incidents, saying it did not want to deter voters.
Two BBC reporters were among a group of journalists briefly detained and questioned by police in Kabul on Thursday for violating the ban.
Some had videotapes confiscated before being released.
- 17 million eligible voters
- Polls opened at 0700 (0230 GMT) and close at 1600
- As well as presidential polls, voters choosing between 3,000 candidates for 420 seats in provincial councils
- Official preliminary results not expected for two weeks but may be earlier indications
- 300,000 troops on patrol (including 100,000 foreign troops)
- 250,000 observers and journalists
- First polls organised by Afghans themselves, but with international support
Opinion polls suggest support for Hamid Karzai, one of more than 30 candidates, is at around 45%, with his former foreign minister, Abdullah Abdullah, in second place with 25%.
His other two main opponents are the independent candidate Ashraf Ghani Ahmadzai and ex-World Bank official Ramazan Bashardost.
Hamid Karzai, Afghan president
Voting in Kabul shortly after polls opened, Mr Karzai urged all Afghans to cast ballots in defiance of the insurgents.
"God willing, this will be for peace, for progress, and for the well-being of the Afghan people. Vote. No violence."
Also voting, Mr Abdullah called it a "day of change, a day of hope" - but fellow contender Mr Bashardost said he had washed off the supposedly indelible ink used to identify people who have voted.
"This is not an election, this is a comedy," Mr Bashardost said, calling on authorities to stop the election.
But his claims were rejected by the Independent Election Commission.
Official preliminary results are not expected until 2 September but there may be earlier indications of the results.
If the winning candidate fails to gain more than 50% of the vote on Thursday, there will be a second-round run-off in October.
We were told to get down, to get into safety. After that we went back out and we heard in total six other explosions until about 0830.
I had presumed that would mean people would be less keen to vote. I was wrong. We went to a high school, one of the men's voting centres. There were queues coming out of every room. People we spoke to were extremely enthusiastic about voting. They were all supporters of President Hamid Karzai.
They said they were not scared by the Taliban's threat to chop off their fingers if they were found with ink showing that they voted, and they were not scared by the Taliban's bombs and rockets.
Are you voting today in Afghanistan? What is the atmosphere like in your town, or at your polling station? Are you concerned about safety? Are you an Afghan voter living abroad? Send us your comments.
Have you had your thumb inked? You can send your pictures to email@example.com or text them to +44 7725 100 100. If you have a large file you can upload here.
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