Image caption Afghan security forces are scheduled to take control in 2014

The last of 33,000 extra US soldiers sent to Afghanistan by President Barack Obama more than three years ago have left the country, the Pentagon says.

They were deployed with the aim of pushing back the Taliban and allowing Afghan government forces time to take over the security of their own country.

Some 68,000 US service personnel remain as so-called insider attacks by Afghan soldiers and police increase.

In the latest violence, a bomb killed five members of the same Afghan family.

Two women, two girls under the age of eight and a man died after a roadside device exploded under their car in the Dehrawood district of Uruzgan province, Afghan officials said.

Abdollah Hemat, spokesman for the governor of Uruzgan, told the Afghan Islamic Press news agency that the dead man was a civilian and not an employee of the government.

No group said it had carried out the attack, but Mr Hemat blamed "the enemies of Afghanistan", a term used by Afghan officials to refer to Taliban insurgents.

Roadside bomb attacks are frequently carried out by the Taliban fighting against Nato forces and the government of President Hamid Karzai.

'Milestone'

US Defence Secretary Leon Panetta announced the withdrawal in a statement, saying an important milestone had been reached.

Afghan 'green-on-blue' attacks 2007 - 2 attacks, 2 Isaf soldiers dead

2008 - 2 attacks, 2 dead

2009 - 6 attacks, 10 dead

2010 - 6 attacks, 20 dead

2011 - 21 attacks, 35 dead

2012 (so far) - 36 attacks, 51 dead Source: International Security Assistance Force (Isaf) What lies behind Afghanistan's insider attacks?

He insisted the surge had been a success, both in terms of driving back the Taliban and damaging its al-Qaeda allies.

"The surge accomplished its objectives of reversing Taliban momentum on the battlefield, and dramatically increased the size and capability of the Afghan National Security Forces," Mr Panetta's statement said.

"This growth has allowed us and our Isaf coalition partners to begin the process of transition to Afghan security lead, which will soon extend across every province and more than 75% of the Afghan population.

"At the same time, we have struck enormous blows against al-Qaeda's leadership, consistent with our core goal of disrupting, dismantling and defeating al-Qaeda and denying it a safe-haven."

Transition to Afghan security control was on track to be completed by the end of 2014, Mr Panetta added.

US forces in Afghanistan peaked at about 101,000 last year with the number reduced incrementally in recent months.

So far this year, 51 members of the coalition (Isaf) have been killed in so-called "green-on-blue" attacks by rogue members of the Afghan security forces, or people dressed in their uniforms.

Mr Panetta has described such attacks as the "last gasp" of the Taliban but other US military leaders have asked about the impact they have on their troops.

Gen Martin Dempsey, chairman of the US joint chiefs of staff, called such attacks a "very serious threat" to the campaign, adding: "Something has to change."

On Tuesday, Nato announced it was restricting operations with Afghan troops. Only large operations will now be conducted jointly, with joint patrols evaluated on a case-by-case basis.

Nato said these were "prudent, but temporary, measures to reduce our profile and vulnerability".

Nato commanders have been frustrated that the Afghans have not done more to stem the rise in attacks, analysts say.