GHAZNI, Afghanistan: Six Afghan police were killed Wednesday when Taliban attacked their checkpoint, a brazen assault likely to raise fresh security questions as the United States prepares a troop drawdown.

The Taliban, which is leading a nearly 10-year war against the Afghan government and US-led foreign troops, claimed responsibility for the attack in Qarabagh district about 120 kilometres (75 miles) southwest of Kabul.

“The attack started at around 7:00 am and six police officers were killed during a gunfight with the attackers,” Sayed Amir Shah, the head of Afghanistan's intelligence agency in Ghazni province, told AFP.

“The gunfire is still ongoing,” Shah said.

Mohammad Ali Ahmadi, the deputy provincial governor of Ghazni, confirmed the toll. “Police teams have gone to the area and the clashes between police and insurgents are still ongoing,” he said.

The assault came just hours before President Barack Obama is to use a prime time speech to order a US troop drawdown from Afghanistan, which one official said would likely see 10,000 soldiers back in America this year.

Taliban spokesman Zabihullah Mujahid claimed responsibility for the attack in a message sent to AFP. On June 19, three police were killed in a similar insurgent attack on their checkpoint in the same district.

Obama's address may come to be seen as the moment when Washington began to disengage from Afghanistan, after a bloody war that has become increasingly controversial in the wake of Osama bin Laden's killing in Pakistan last month.

Obama will stick with his vow to begin pulling out US forces after an 18-month troop surge, but apparently heed Pentagon warnings that an overly swift withdrawal could imperil hard-won gains against the Taliban.

A senior defense official said on condition of anonymity that the president would “likely” order the return of about 5,000 troops this summer and 5,000 more by the end of the year.

Another 20,000 troops, part of a 30,000-strong surge ordered in December 2009, would be withdrawn by the end of next year, meaning elevated force levels would remain through two more Afghan summer fighting seasons.

It would still leave more American troops in Afghanistan than when Obama was elected to office in November 2008.

But war sceptics argue that after the deaths of more than 1,600 US service personnel and at a cost of nearly dollar 10 billion a month, the American commitment is unsustainable at its present size of 99,000 US troops.

All 130,000 Nato-led international combat forces are due to leave Afghanistan by the end of 2014. A limited withdrawal of troops is expected to begin this July.