The United States has asked for New Zealand's moral support if it goes ahead with a military strike in Syria.

New Zealand Prime Minister John Key says the government isn't ready to make a decision on that.

"We've said we would have to assess all the circumstances and processes prior to the point that it (a military strike) occurs," he said on Monday.

"We're obviously very concerned by the use of chemical weapons in Syria, this is a great human tragedy."

Mr Key says US Secretary of State John Kerry spoke to Foreign Minister Murray McCully over the weekend.

"He said if there's military action, one of the things they would like us to consider is whether New Zealand could lend moral support."

Mr Key says there have been no requests for any other kind of support.

Parliament will have an opportunity to debate the issue but Mr Key says cabinet will decide whether or not to offer moral support.

US President Barack Obama is going to seek the approval of Congress for a military strike.