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President Barack Obama has officially vetoed a bill to approve the Keystone XL pipeline, marking his third rejection of congressionally approved legislation during his six years in office.

In the veto message, Obama said that the bill "attempts to circumvent longstanding and proven processes for determining whether or not building and operating a cross-border pipeline serves the national interest."

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"[B]ecause this act of Congress conflicts with established executive branch procedures and cuts short thorough consideration of issues that could bear on our national interest -- including our security, safety, and environment -- it has earned my veto," Obama said.

The president notified the Senate of the veto on Tuesday afternoon.

The veto, which was long expected, came the same day that the GOP-dominated Congress formally submitted the bill to Obama, although it was passed by both chambers of Congress before the week-long Presidents Day recess.

The White House has said that the president opposes the bill because it would cut short an ongoing review process of the project by the State Department. Obama has also expressed some skepticism about how many jobs the pipeline would create.

Senate Majority Leader Mitch McConnell said Tuesday that the Senate will attempt to override the veto no later than March 3. Congress could override the veto if two-thirds of both the House and the Senate vote to do so, but lawmakers aren’t expected to reach that threshold.

Republicans have accused the president of bowing to pressure from environmental activists who oppose the project. These advocates say the pipeline could cause spills and argue that it would increase the nation’s dependence on fossil fuels.

In a statement, House Speaker John Boehner called the veto "a national embarrassment."

"The president is just too close to environmental extremists to stand up for America's workers. He's too invested in left-fringe politics to do what presidents are called on to do, and that's put the national interest first," he said.

- Carrie Dann