Military commanders in Afghanistan have put a virtual news blackout on a coalition operation against suspected Taleban and al-Qaeda fighters in the eastern Paktia province.
British and US forces have joined Australian troops who came under attack on Thursday from suspected Taleban and al-Qaeda fighters in south-eastern Afghanistan.
The BBC's Paul Adams who is at Bagram airbase says the military is remaining tight-lipped on the progress of the operation, codenamed Condor, but that helicopter gunships and A-10 tank busters were flying in and out of the base all day.
There have been some local reports that the fighting may have been triggered by Australian forces blundering into a dispute among local tribesmen.
Enemy contact
Speaking about Thursday's fighting, Brigadier Roger Lane, the top British commander in Afghanistan, said the Australian troops battled a "substantial force".
"I can confirm that the coalition has made contact with the enemy and that some have been killed," he said.
Brigadier Lane added that no coalition casualties had been reported.
He said the fighting was taking place in a mountainous area at an altitude of 2,400 metres (8,000 feet), but declined to be more specific.
Our correspondent has been told that British troops are on the ground, American aircraft are providing cover, and that the mission is expected to last a few days.
Military blunder?
There have been some reports from the area where Operation Condor is taking place that the Australian forces may have blundered into a dispute among local tribesmen – a suggestion a British spokesmen could not rule out.
Our correspondent says the operation could still prove a success or an embarrassment.
In recent days, the US-led coalition has been stepping up its search in eastern Afghanistan for al-Qaeda and Taleban fighters.
The fighters are thought to have dispersed into small groups and blended in with local residents or fled across the border to neighbouring Pakistan.
Coalition troops had reported no enemy contact for several weeks.
On Monday, British-led forces ended a two-week search operation in eastern Afghanistan saying they had dealt a "significant blow" to al-Qaeda's ability to mount future strikes by blowing up a big ammunition dump located in several caves in Paktia province.
That operation involved about 1,000 British and Afghan troops and was backed by American air support and special forces.
Illness spreads
However, a local anti-Taleban commander later cast doubt on the British account of the operation, saying the arms no longer belonged to al-Qaeda and were being held in reserve for Afghanistan's future army.
Meanwhile, the mystery illness which has affected British army medical workers in Afghanistan has now spread to operational staff.
A further 22 cases have been reported, all from outside the original group of three-hundred still under quarantine.
The illness, which causes vomiting and stomach pain, broke out earlier this week at a field hospital at the Bagram air base.
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