New Zealand''s prime minister said Monday that he wants an exit strategy before sending the country''s elite Special Air Service combat troops back to Afghanistan as the U.S. has requested.

Prime Minister John Key said that sending the commandos for a fourth tour of duty in Afghanistan "would be a very hard decision, not something we would take lightly."

New Zealand Foreign Minister Murray McCully said the U.S. formally requested that New Zealand send its Special Air Service troops back into Afghanistan following a meeting he had with U.S. Secretary of State Hillary Rodham Clinton in Washington earlier this month.

Key said Monday he had not seen details of the U.S. proposal, but said, "If we were to do something, it would be part of a long-term exit strategy."

McCully said New Zealand would consider resource and capacity issues before making a decision on the U.S. request. The deployment also depends on other conflicts in the South Pacific.

The New Zealand commandos have already done three tours in southern Afghanistan since the 2001 U.S.-led invasion to topple the Taliban''s hard-line Islamist regime for sheltering al-Qaida terrorist leaders.

New Zealand also has 140 troops serving in a provincial reconstruction team in the Afghan province of Bamiyan, northeast of the capital, Kabul. The team has been there since 2003 and is to remain until at least September 2010.