WASHINGTON (AP) — North Dakota Democrat Heidi Heitkamp says she cannot support a Senate measure authorizing military force against Syria.

In a statement on Monday, the freshman lawmaker is pressing for a diplomatic or alternative approach to the crisis. Heitkamp said the United States should not act unilaterally and needs other nations to prevent the use of chemical weapons in Syria.

Heitkamp and Democratic Sen. Joe Manchin of West Virginia, who also opposes the use of U.S. military force, have been working on an alternative that would give Syrian President Bashar Assad 45 days to sign onto an international ban on chemical weapons.

An Associated Press survey finds the Senate basically even, with a third supporting military action, a third against and the rest undecided.