Three U.S. Senators visiting Afghanistan have expressed concern that U.S. President Barack Obama's planned withdrawal of 33,000 American troops from the country by September 2012 could hamper efforts to defeat the Taliban.

Republican Senators John McCain and Lindsey Graham, and Independent Senator Joe Lieberman, commented Sunday during a news conference in the Afghan capital, Kabul.

McCain called the drawdown plan “unnecessary risk” that is not supported by U.S. military commanders.

The senators also called for a stronger stance from Pakistan. They said Washington wants good relations with Islamabad but that Pakistanis have to decide whether, as Lieberman put it, “they want to be our friends or our enemies.” Pakistan is home to many of the insurgent groups NATO forces are currently fighting in Afghanistan.

Also Sunday, British newspapers said Prime Minister David Cameron will announce the withdrawal of at least 500 troops from Afghanistan by the end of 2012.

Britain has the second-biggest foreign contingent in Afghanistan — some 9,500 troops — with the majority stationed in southern Helmand province, one of the most violent areas.

The chief of staff of Germany's armed forces said Sunday that Berlin will also reduce its troop levels in Afghanistan by about 500 at the end of the year. Germany has about 5,000 troops in northern Afghanistan.