White House Chief of Staff Denis McDonough, saying the United States is at war with ISIS, today expressed confidence in the Iraqi army to take on the militant Islamic group even though it has failed to do so effectively in the past.

"There is now a new multi-ethnic government in Baghdad. They will support a unified, capable multi-ethnic Iraqi force so that they can take this fight to ISIL," McDonough said today on "This Week."

ISIL is also known as ISIS or the Islamic State.

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The White House chief of staff was asked by ABC News's Martha Raddatz if there is a limit how many U.S. troops will be sent to Iraq.

"I'm not in a position right now to tell you limits one way or the other," he said.

Secretary of State John Kerry will have "news" this week when he testifies in Congress regarding countries that may join the United States in military action to eliminate ISIS, McDonough said. The chief of staff did not, however, provide details on when the U.S. might take action in Syria.

During a primetime address to the country last week, President Obama laid out his plan to "degrade and ultimately destroy" ISIS, the extremist Islamic group that has snatched territory in Iraq and Syria in recent months and is responsible for the grisly executions of two American journalists and most recently David Haines, a British citizen who was kidnapped last year.

Raddatz asked McDonough if the executioner had been identified.

"Obviously we're doing everything we can to find that out and everything we can to continue to keep the heat on ISIL," McDonough said.

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