WASHINGTON — U.S. Sen. Susan Collins, R-Maine, said late Tuesday that she opposed a resolution authorizing U.S. missile strikes inside Syria and instead urged continued diplomatic efforts to avoid military intervention.

After a week of closed-door briefings on the Syrian issue, Collins said she could not support a Senate Foreign Relations Committee resolution authorizing military force. Collins made the statement on a day of frenzied activity on Syria and after it became clear that a Senate vote tentatively planned for later this week would likely be delayed amid ongoing diplomatic negotiations.

“I have many concerns about deepening U.S. involvement in the Syrian conflict because our country could find itself slowly entangled in an increasingly dangerous and protracted civil war,” Collins said in a statement Tuesday evening, just prior to President Obama’s speech on the issue.

“I don’t think U.S. involvement would end with just one military strike,” Collins said. “The United States should be aggressively pursuing a diplomatic solution such as the one put forward by the Russians. It certainly is preferable to launching a military strike on a country that has not attacked us.”

Collins wasn’t the only member of Maine’s congressional delegation to state her position for the first time on Tuesday. Earlier in the day, U.S. Rep. Mike Michaud said he could not support a “unilateral military solution” to the situation in Syria.

“Based on the information I’ve now had a chance to see, I am not convinced that we should take military action,” the 2nd District Democrat said in a statement. “In addition, I have heard from thousands of Mainers who have told me they do not want to get embroiled in another war in the Middle East.”

Additionally, Democratic U.S. Rep. Chellie Pingree of the 1st District made clearer her opposition to military strikes following the president’s speech to the American public.

“It was important that the president took the time to lay out his case to the American public tonight as well as asking the Congress to delay any votes,” Pingree said in a statement after the president concluded his remarks.

“But I continue to believe that military intervention in Syria is not in the best interest of the United States and nothing I heard tonight changes my view of that.”

Syria once again dominated discussion in Washington on Tuesday as Obama made his case to Democratic and Republican senators during separate luncheons in the Capitol. The president explained his administration’s argument for targeted military strikes but also asked the Senate to delay a vote while the U.S. negotiates with Russia and other nations on a proposal to have Syrian President Bashar Assad hand over all chemical weapons to an international body.

U.S. Sen. Angus King of Maine, an independent who caucuses with the Democrats, said after the luncheon that the president made a strong argument for his case.

Both King and Collins have received numerous classified briefings as members of the Senate Intelligence Committee. They have also had one-on-one meetings with top intelligence or administration officials.

Unlike Collins, however, King was still unprepared to take a position on the issue of targeted strikes by the U.S. King said in an interview early Tuesday evening that he was still concerned about the potential ramifications of U.S. involvement.

King said the discussions with the Russians were encouraging because they could remove the Assad government’s ability to use chemical weapons while reducing the risk of the weapons falling into to the hands of terrorist groups working with the rebels if the Assad government should fall.

“This is a very important development,” King said. “We don’t know if it is going to work and we don’t know how far it is going to go.”

Washington Bureau Chief Kevin Miller can be contacted at 317-6256 or at kmiller@mainetoday.com