"Not to act is to act. Not to act would send a very dangerous message . . . to dictators all over the world that they can use chemical weapons, and maybe other weapons of mass destruction, without any consequences," Rasmussen said.
To that end, he said there was "strong political support" among alliance members for military action in Syria.
"Allies have consulted and I think there is consensus that we need a firm reply," to the Assad regime's alleged use of chemical weapons, he added.
Rasmussen's comments come as the White House is attempting to shore up support for military action in Syria, both at home and abroad.
On Monday, the White House released a revised list of U.S. allies who are publicly backing armed intervention in the country.
The current list of international signatories who are backing the administration's Syria policy currently stands at 24.
Despite the growing number of foreign countries signing onto the White House statement, only one -- France -- has publicly agreed to provide military support for possible American-led action in Syria.
In August, the British Parliament soundly defeated an effort by U.K. Prime Minister David Cameron to authorize British forces to take action in Syria, alongside American forces.
While insisting armed intervention is the only way to prevent another chemical attack, Rasmussen stopped short of committing the alliance to any U.S. action.
"NATO already plays its part as a forum for consultation among allies," he said. "And of course we keep the situation in Syria under review."
White House has all but abandoned efforts to secure a United Nations mandate for military action in Syria, due to Russia and China's opposition to strikes against their top ally in the Mideast.
President Obama is seeking congressional authority to take military action against Assad's forces, in retaliation for the regime's alleged use of chemical weapons against anti-government rebels in the country.
Use of those weapons, Obama claims, crossed a so-called "red line" that would trigger an armed response from U.S. forces.
Obama has maintained the White House has the authority to carry out strikes against Syria, without the blessing of Congress.
However, the president opted to seek lawmakers' approval, to ensure any action taken has the full support of the American people.
In the U.S., finding support on Capitol Hill has proven difficult, with members in both parties saying they want to avoid getting the U.S. involved in another conflict in the Middle East.
Several polls last week also found most Americans oppose intervention. Gallup found that 51 percent opposed a strike, and 13 percent were undecided. A Washington Post/ABC News poll found 59 percent opposed a strike. And Pew’s survey showed 48 percent disapproved.