Top US lawmakers on Sunday slammed President Barack Obama's military drawdown plans for Afghanistan as "risky", unsupported by his military commanders and a threat to progress made in the last year.

Withdrawal at the rate Obama has planned on -- including the removal of 33,000 surge troops by the end of next summer -- "is an unnecessary risk and that is why there was no military leader who recommended it", Republican Senator John McCain said during a visit to Kabul.

Joined by fellow Republican senators Lindsey Graham and Joe Lieberman in the Afghan capital, the trio spoke to media after visiting US troops.

Graham described progress in parts of the war-torn country as "really stunning" but warned that "all the gains are still reversible".

"What I'm mostly concerned about is that the accelerated withdrawal of surge forces has created a perception that we are leaving," said Graham.

"Withdrawal is what the enemy wants to hear and our goal is to make sure they don't hear withdrawal and the Afghan people don't hear withdrawal," he later added.

Both General David Petraeus and Admiral Mike Mullen, the chairman of the Joint Chiefs of Staff, have said Obama's plan was more "aggressive" than they had recommended.

Obama late last month said 10,000 troops would leave this year and all 33,000 personnel sent as part of a surge ordered in late 2009 would be home by next summer, leaving a US force of some 65,000.

There are currently up to 150,000 foreign forces in Afghanistan, including about 99,000 from the United States.

Obama has indicated a series of drawdowns until Afghan forces assume full security responsibility in 2014.

Speaking to CNN's "State of the Union" McCain also lambasted the US leader for not providing adequate troops for the initial 2009 surge -- "He didn't give them the full complement they needed. It was about 10,000 short, which then necessitated a second fighting season," he said.

"Look, I question whether this was the right decision or not, but I can't question the president's patriotism," he added.

Obama's announcement pleased practically nobody in Washington -- liberals were left wanting more, Republican hawks complained he was going too fast, and top Pentagon officials felt snubbed for having much of their advice overruled by the White House.

The military case for the drawdown, with Obama saying the war aims he set in 2009 had been largely met, was also seen as highly political, as it foreshadowed the argument he will make to voters next year as he runs for a second term.

The Washington debate comes as the US-led coalition hankers for a resolution to the nearly decade-long war, but amid dismal relations between the US and its key War on Terror ally Pakistan.

The Taliban's leadership is believed to reside in Pakistan and the nuclear power is seen to use the insurgent group as a bargaining chip in any regional settlement of power, complicating Western attempts to broker peace.

"Until Pakistan begins to help, its gonna be very difficult," said Graham.

"So our job as members of the Senate is to tell the Pakistani military: You need to choose. You need to choose who you want your friends to be and who you want your enemies to be... Too much is at stake to let this drift any further."