Sen. Joe Manchin III (D-W. Va.)speaks to the media after a vote on Capitol Hill in December 2012. (REUTERS/Joshua Roberts)

Updated and corrected

Sen. Joe Manchin III (D-W. Va.) announced Wednesday that he will vote against legislation authorizing President Obama's plans to arm and train Syrian rebel forces, saying he hasn't been convinced that a new U.S. military effort in the Middle East will succeed.

"I cannot and will not support arming or training the Syrian opposition forces," Manchin said in a Senate floor speech.

The senator's decision means he will vote against a short-term spending bill designed to keep the federal government open when the new fiscal year begins on Oct. 1. The House is expected to approve the bill later Wednesday after amending it to include explicit authorization of Obama's plans to counter the growing threat of the Islamic State terror group.

Manchin said he came to his decision after consulting military and foreign policy experts and attending classified briefings with top national security officials.

"But most importantly I studied our history," he said. "We have been at war in that part of that world for the past 13 years. If money and military might could have made a difference, it would have by now."

Authorizing Obama's plans to train and equip rebels means "we will be involving ourselves in a ground conflict we cannot resolve," he added later.

Manchin is serving his first term in the Senate and has usually taken a skeptical approach to expanding U.S. military operations overseas.

In an interview with The Washington Post last week shortly after Obama's national address on his new military strategy, Manchin raised concerns about partnering with rebel forces in Syria. "No one’s convinced me that they can identify friend or foe in that part of the world right now," he said. "Anything that I have been able to witness is that no matter who we are ends up those arms are used against sooner or later. That’s a sad scenario."

Manchin is one of a small handful of Democratic senators expected to vote against Obama's military plans. Already Sen. Mark Begich (D-Alaska) has said he will oppose any new military operations in the Middle East. Sen. Christopher Murphy (D-Conn.) also has raised concerns, but not yet signaled how he will vote.

Another senator who has raised concerns, Tim Kaine (D-Va.), said in an interview with The Post Wednesday morning that he plans to support Obama's strategy because Senate leaders are planning to hold an expanded debate on the future of military action in the Middle East later this fall after the November elections. Kaine had previously raised concerns that Congress would be rushing to authorize Obama's plans without a full debate and argued that it would be unconstitutional for Obama to proceed without explicit congressional authority.

CORRECTION: An earlier version of this report suggested that Sen. Mark Udall (D-Colo.) opposes Obama's plan to train and equip Syrian rebels. Aides say that the senator plans to support it.