The Pentagon has abandoned its failed $500 million program to train "moderate" Syrian rebels in favor of ramping up support for established and proven forces — including Kurdish fighters — a decision that comes on the heels of the White House's admission that building a force from scratch to combat the Islamic State in Iraq and the Levant (ISIL) was "a more difficult endeavor than we assumed."

Pentagon spokesman Peter Cook announced the strategic overhaul on Friday, saying in a statement that the U.S. will now "provide equipment packages and weapons to a select group of vetted leaders and their units" who are "motivated to take back Syrian territory from ISIL."

He specifically mentioned the Kurds, saying that the U.S. will build on progress achieved by joint U.S.-Kurdish operations against ISIL in northern Syria. The high-profile success in the Turkish border town of Kobane — where American air support and arms shipments helped Kurdish militias drive out ISIL earlier this year — will serve as a model, he said.

Speaking at a press conference in London earlier on Friday, Defense Secretary Ashton Carter admitted that he "wasn't satisfied with the earlier efforts" of the U.S. program. But "the work we've done with the Kurds in northern Syria is an example of an effective approach. That's exactly the kind of example that we would like to pursue with other groups in other parts of Syria, going forward."

In a conference call with reporters, White House Deputy National Security Adviser Ben Rhodes insisted that the U.S. was "not ending the [train and equip] program but pausing elements." But officials confirmed that the U.S. will, in fact, stop recruiting "moderate" Syrian rebels for training programs hosted in nearby countries, including Jordan and Saudi Arabia. Instead, individual leaders — rather than groups of fighters — will be vetted to receive arms, which will not include anti-aircraft weapons or other heavy artillery.

Friday's announcement comes more than a week into a bold Russian intervention on behalf of Bashar al-Assad's regime, which has been on the defensive in several key battlegrounds. Since Moscow started strikes against Syria's rebels — including some reportedly backed by a separate, covert CIA program — President Barack Obama has been under pressure to respond more forcefully. But he isn't willing to commit U.S. troops to Syria and, analysts say, increasingly sees minimal strategic gain in toppling Assad, which could expand the power vacuum that allowed a greater threat, ISIL, to metastasize.

The new strategy, which focuses exclusively on combating ISIL, follows a series of very public embarrassments that befell Obama's first batch of trained rebels. The $500 million program was intended to train more than 5,000 rebel fighters, who administration officials hoped would counter both ISIL and, to a lesser degree, Assad.

But only about 100 trained fighters were deployed in Syria, reportedly because of difficulties vetting such large numbers. The first batch was promptly attacked by hard-line rebels upon crossing the border, and others disbanded or were killed in combat. As of September, a top U.S. general admitted, only "four or five" were still fighting in Syria.

Then last week, it was reported that one of the U.S.-trained commanders handed over American arms and vehicles to fighters from Jabhat Al-Nusra (the Nusra Front), Al-Qaeda's affiliate in Syria. The incident underlined the fundamental pitfall of the U.S. strategy: The "moderate" rebels that the U.S. hoped would focus their fire on ISIL were often inclined to work — and even share weapons — with hard-line, anti-American groups that were aligned against both ISIL and the Syrian government.

In that light, the decision to expand U.S. aid for the Kurds will be welcomed by critics of Obama's Syria strategy who have long pointed out that Kurdish militias are the only proven, pro-Western faction fighting ISIL in Syria. The Kurds have also largely avoided confrontation with the regime, preferring to carve out an autonomous territory in Syria's north, and can therefore be relied upon to focus on ISIL.

Washington has been hesitant to fully embrace Kurdish fighters because of political complications posed by the group's close ties in Turkey with the separatist PKK insurgency, which Washington and Ankara consider a terrorist organization. Whereas the U.S. is willing to overlook the Syrian Kurdish PYD's relationship with the PKK, Turkey considers Kurdish separatism — both inside and outside its borders — a greater threat to its domestic security than ISIL.

In recent months, an enlivened PKK has carried out a spate of attacks on Turkish soldiers, and Ankara has responded by launching airstrikes on Kurdish targets in Turkey and Iraq.

It isn't clear how Turkey will respond to heightened U.S. support for Syria's Kurds. It has long been frustrated by Washington's shift in priorities and its declining commitment to the rebel cause. Specifically, the U.S. has not heeded Turkey's call for help in establishing a buffer zone in Syria along their border, mainly to stem the flow of refugees and provide breathing space for Sunni Arab rebels but also to marginalize Kurdish forces.

Plenty more questions remain about the program. For one, officials have declined to name any groups the Pentagon planned to aid apart from the Kurds. The Pentagon wants to build on the successes of Kobane "and work with groups on the ground and provide more equipment in combination with airstrikes," Christine Wormuth, the undersecretary of defense for policy, told reporters on a conference call. "We've worked with some of these groups and know who they are."

Meanwhile, hawkish U.S. lawmakers reiterated their fierce criticism of Obama's policy in Syria. They blame the president's limited and delayed support for the "moderate" rebels as the reason Assad has clung to power after four years and ISIL has seized nearly 50 percent of the country. Some have even called for ground troops to be deployed.

"The administration has had a weak, inadequate policy in Syria and a weak, inadequate policy against" ISIL, said Rep. Mac Thornberry, R-Texas, the chairman of the Armed Services Committee, in a statement. "Adjusting one program, even if it were successful, will not solve the problem."