U.S. President Barack Obama says questions need to be answered before the U.S. increases its use of crude from the Canadian oilsands through projects like proposed Keystone XL project.

"These tarsands. There are some environmental questions about how destructive they are, potentially, what are the dangers there and we've got to examine all those questions," Obama told an energy town hall Wednesday in Fairless Hills, PA.

"So we've got to do some science there to make sure that the natural gas that we have in this country, we're extracting in a safe way. The same thing is true when it comes to oil that's being piped in from Canada, or Alaska, for that matter. We've got to do these evaluations."

Last month, the U.S. State Department announced a supplemental draft environmental impact statement and comment period to evaluate TransCanada's $13 billion US Keystone XL pipeline, which is proposed to bring oil from Alberta to Texas.

In his response to a man who identified himself as a Canadian and used the term "tarsands" in his question, Obama said he cannot comment specifically on the project since it is now under review.

"If it looks like I'm putting my fingers on the scale before the science is done, then people may question the merits of the decision later on," Obama said. "So I'm not going to get into the details of it."

Canadian approvals for the project are already in place.The State Department is responsible for approving the U.S. portion of the project since it would cross the U.S.-Canada border.

This week, an editorial in the New York Times slammed the project and said it poses "enormous" enviromental risks to both Canada and the U.S.

With files from The Canadian Press