At least 140 Nato troops - including 19 British soldiers - have been killed in so-called green on blue attacks in the Afghanistan conflict.
ITV News has obtained exclusive footage showing that for the first time women are playing a key role in the new look Afghan police force.
As British forces end their command of Helmand, there is growing evidence that the conflict is having an unrelenting toll on children.
Women voters have been lining up at polling stations across Afghanistan, defying a threat of violence by the Taliban to cast ballots in what promises to be the nation's first democratic transfer of power.
The Taliban warned civilians ahead of the election they would be targeted if they try to vote, and dozens died in a spate of attacks in the preceding weeks.
Long queues continue to form outside polling stations around Kabul, as people defied Taliban threats of violence to cast ballots in what promises to be the country's first democratic transfer of power.
As international combat forces prepare to withdraw by the end of this year, the country is so unstable that the very fact the crucial elections are being held is touted as one of the few successes in Mr Karzai's tenure.
Nearly 200,000 Afghan security forces are out protect polling stations and voters from threatened Taliban attacks.
Four voters were wounded in an explosion at a polling station in the southeastern province of Logar.
"The blast took place close to a polling station which is a school building and wounded four voters, one critically," Abdul Hameed, governor of the province's Mohammad Agha district, told Reuters.
It was the most serious attack so far on an election that Taliban insurgents had vowed to derail, branding it a 'US backed sham'.
Yousaf Nuristani, chairman of the Independent Election Commission has called on the people of Afghanistan to "come out and vote for their favourite candidates," as voting begins for millions of Afghan citizens across the country.
Presidential candidates Ashraf Ghani and former Afghan foreign minister Zalmai Rassoul voted among others at polling stations to succeed Hamid Karzai as president.
In the Afghanistan elections a candidate must secure more than 50 percent of valid ballots, failing which the top two candidates go into a run-off. The three frontrunners all enjoy similar levels of support, so a second round of voting is likely.
The time frame for all voting are as follows:
- Vote counting: April 6 to 20
- Preliminary results: April 24
- Final results announcement: May 14
- (Source: Independent Election Commission)
Here are some of the key points surrounding today's election:
- 28,500 polling centres opened, with 10 percent closing due to security.
- It will require around 3000 donkeys to carry ballot boxes due to terrain.
- There are 12 million eligible voters.
- Afghan authorities deployed 352,000 forces to provide security.
- Taliban called the elections a 'US backed sham.'
In the Ghorband Valley of Parwan province, some polling stations have come under mortar and machine-gun fire, but no casualties were reported and voting has no major disruptions - report NBC.
A few polling stations in eastern #Afghanistan have come under mortar fire, an Afghan official tells us, but no major disruption to voting.
Despite Taliban threats, voting in #Afghanistan going ahead. Let's hope that tonight Afghans will be counting votes, not casualties.
An account purportedly belonging to the Taliban sent a string of tweets claiming disruptions and violence at polling stations:
All voting booths closed in Jurm district (#Badakhshan), one station open but under assault since morning
Polling stations opened at 7am and are slated to close at 4pm local time.
Afghans queued up to vote in the county's presidential election today, despite the threat of violence from Taliban insurgents.
"I am here to vote and I am not afraid of any attacks," said Kabul resident Haji Ramazan at a polling station in the capital. "This is my right and no one can stop me."
"I call on the people of Afghanistan to prove to the enemies of Afghanistan that nothing can stop them," Yousaf Nuristani, chairman of the Independent Election Commission told reporters after he cast his own vote in Kabul.
Hamid Karzai, the incumbent, is not allowed to run for the presidency again by the constitution.
But after 12 years in power he is widely expected to retain influence through politicians loyal to him.
He appeared relaxed and smiled for reporters as he cast his vote today.
About 12 million are eligible to vote, and there are eight candidates, with former foreign ministers Abdullah Abdullah and Zalmai Rassoul, and former finance minister Ashraf Ghani the favourites.
Millions of Afghans will vote today in an historic presidential election that the first democratic transfer of power in the country's history.
Of the eight candidates, the three favourites are former foreign ministers Abdullah Abdullah and Zalmay Rassoul, and former finance minister Ashraf Ghani.
An unprecedented level of security is in place after the Taliban vowed to "use all force at its disposal to disrupt these upcoming sham elections."
Dozens of people have been killed in a spate of violence leading up to the vote.
Veteran photographer Anja Niedringhaus and acclaimed reporter Kathy Gannon were rushed to hospital after they were shot while sitting in the back of car by an Afghan policeman, a hospital director has said.
– Khost hospital director Abdul Majeed Mangal
Today around 11:00am [6.30am GMT] we received two foreign female journalists who were working for a news agency.
One was killed and the other was wounded seriously.
The wounded journalist who is about 60 years old, she is in critical condition and our surgical team is providing her first aid.
Photographer Anja Niedringhaus, 48, was killed and reporter Kathy Gannon, 60, wounded while they were sitting in the back of a car, Associated Press said.
Anja Niedringhaus, an acclaimed German photographer who had covered conflict zones including Kuwait, Iraq, Libya, Gaza and the West Bank, was killed instantly, according to an AP Television freelancer who witnessed the shooting.
Canadian reporter Kathy Gannon, who is based in Islamabad and has covered war and unrest in Afghanistan for 30 years, was shot twice and was receiving medical help, the AP said. Kathy Gannon underwent surgery in the eastern city of Khost. .
The operation was described as successful and Gannon's condition was stable, AP said