America's military chief has flagged the possibility of sending more US troops to Afghanistan on top of 68,000 approved by the Obama Administration, warning that Americans should brace for more US casualties.
Over the past fortnight there has been speculation that there is an unofficial ceiling on the US commitment of troops to Afghanistan, after National Security Adviser General Jim Jones was reported as telling commanders in Afghanistan that President Barack Obama was likely to react badly to a troop request.
But Admiral Mike Mullen has denied there is a cap on the US commitment in Afghanistan, which was identified by President Obama as a priority.
"There is not a ceiling on troop levels," Admiral Mullen, head of the Joint Chiefs of Staff, said in a speech to the Centre for Strategic and International Studies on Tuesday.
Admiral Mullen said US General Stanley McChrystal, the recently appointed commander of international forces in Afghanistan, now had all the troops his predecessor had asked for and had been given 60 days to come back with his own assessment of what was needed.
"In the interim he will come back with his assessment and my guidance to him is: 'You tell me what you need, bring it back to Washington and we'll take it from there.' "
But Admiral Mullen also said it was incumbent on the commanders to make sure that every US serviceman in Afghanistan was needed and he foreshadowed that there would be higher casualties in the tough and potentially long fight ahead in Afghanistan.
The deaths of seven US soldiers on Monday were "an indication of expectations that I've had for some time that this fight is going to be tough", he said. "It's going to get tougher before it gets easier."
Admiral Mullen also appeared to qualify last week's estimate that the operations in the southern Helmand province would last weeks, not months, saying on Tuesday: "It's just a beginning and we actually don't know."
He also agreed with the former US ambassador to Afghanistan, Ron Neuman, that Afghanistan posed extra challenges because there was only about a third the number of local security forces compared to the numbers in Iraq - raising questions about holding territory claimed from the Taliban, and the US's longer-term exit strategy.
Admiral Mullen said there were 80,000 in the Afghan army, with authorisation to go to 134,000. But he said that "134,000 might not be right".
The US had reached its goal of 82,000 police, he said, but the "challenge was the quality and training and getting them out there through Afghanistan."
At the time of the US surge in Iraq in 2008, the security forces numbered 600,000.
Afghanistan is a bigger and slightly more populous country than Iraq, with more challenging terrain. Total security force numbers, including NATO, local army and police, total 260,000.