Key allies stand ready to join the United States in military action to defeat Islamic State militants in Iraq, President Obama said at the NATO summit in Wales. (Reuters)

— President Obama said Friday that a new NATO-directed coalition could reach out to some Syrian rebels as possible proxy fighters in a sharply expanded push to battle Islamic State militants.

The potential outreach to the rebels — which would mark a significant shift in Western intervention inside Syria — is part of a multilayer effort to combat the group formerly known as the Islamic State of Iraq and Syria (ISIS). The tactics are expected to stretch beyond the battlefield, such as trying to disrupt the Islamic State’s recruiting and financial networks.

The 10-nation coalition, forged during a two-day NATO summit in Wales, represents the most far-reaching attempt to undercut the Islamic State factions controlling parts of northern Iraq and Syria. It also reflects the depth of Western concerns about the growing threats from the group, which has drawn international condemnation for brutalities that include mass killings and the beheadings of two American journalists.

“The bottom line is that we will do what is necessary’’ to confront the Islamic State, Obama said at a news conference. He offered few specific details on what he described as a “systematic’’ push to weaken and “ultimately destroy’’ the Islamic State in its strongholds in northern Iraq and parts of Syria.

The United States has already launched a series of airstrikes seeking to slow the advance of the Islamic State in northern Iraq and bolster the defenses of Western-allied fighters in Iraq’s nearby Kurdish region.

Obama said there are no plans to deploy U.S. ground troops in the region, and he offered no indications whether aerial attacks on the Islamic State could extend to Syria. But Obama suggested that NATO partners could enlist “moderate” rebel forces in Syria to join the fight against the Islamic State.

Such a plan could also expand direct U.S. support for some of the factions battling Syrian President Bashar al-Assad. Until now, Western aid to Syrian rebel groups has been limited because of fears weapons could fall into the hands of al-Qaeda-linked factions and others in the war-battered country.

A senior Obama administration official said there was consensus among NATO allies that the goal to “destroy” the Islamic State would eventually require action in Syria. But the official said efforts would first concentrate on combating the Islamic State in Iraq.

“Of course when you introduce the Syria equation, it gets much more complicated,” said the official, who spoke on condition of anonymity because of the sensitivity of the issue.

Earlier, Secretary of State John F. Kerry said the multinational alliance possesses “the ability to destroy’’ the militants with a combination of military, diplomatic and financial pressures.

“It may take a year, it may take two years, it may take three years. But we’re determined. It has to happen,” he said.

Kerry and Defense Secretary Chuck Hagel used the summit in Wales to pull together the coalition made up of NATO members Britain, France, Germany, Canada, Turkey, Italy, Poland and Denmark, along with Australia.

Britain, France and Australia are considered the most likely allies to possibly join the United States in more aggressive airstrike campaigns against the Islamic State — at least in Iraq. France and Australia have military outposts in the United Arab Emirates. Britain has a military base in Cyprus in the eastern Mediterranean.

Philip Hammond, Britain’s foreign secretary, said his country had “made no commitment to take part in any airstrikes as yet, but we’ll certainly consider that possibility.”

The coalition also plans to expand efforts to arm and train Iraqi government forces and Kurdish fighters. The alliance would also further coordinate operations to deliver humanitarian aid to refugees who fled as the Islamic State gained ground.

U.S. officials, meanwhile, are pressing other NATO members to share intelligence about the Islamic State — which has drawn thousands of foreign fighters from Europe, North Africa, the United States and elsewhere.

The Obama administration is paying special attention to NATO-member Turkey. The country has been affected by the spillover of thousands of refugees from Syria, but it has also come under criticism for allowing foreign fighters from Europe to cross its borders to join the Islamic State.

Recep Tayyip Erdogan, the Turkish president, met Friday at the NATO summit with Obama, Hagel and Kerry. Hagel also plans to travel to Turkey early next week.

“We have no tolerance regarding the crossings into Syria,” Erdogan told Turkish reporters Thursday in response to accusations that Turkey was not sufficiently blocking suspected militants.

The U.S. military has a large force stationed at Incirlik Air Base, although it is unclear how much Turkish officials would allow the base to become a hub for missions against the Islamic State.

The Obama administration has said the next phase is to secure backing from Arab countries. Although some of those countries have been pressing the White House to act more aggressively against the Islamic State, they have been less eager to advertise their positions or make a show of joining in any military campaigns.

Katie Zezima contributed to this story.