(CNN) U.S. efforts against ISIS could be set to ramp up a notch, as U.S. Defense Secretary Ash Carter told lawmakers Tuesday the Pentagon was looking at stepping up its campaign against the terror group through more special operations forces raids and airstrikes.
Outlining a potential new approach to build momentum in the campaign against ISIS -- yet to be approved by the White House -- Carter spoke of a triple-pronged strategy focusing on "three Rs": raids, Raqqa -- the terror group's de facto capital in Syria -- and Ramadi, the Iraqi city seized by ISIS earlier this year.
So why is the U.S. looking at tweaking its strategy against ISIS in this way -- and has it been prompted by the intervention of a fourth R, Russia?
READ MORE: U.S. weighing 'direct action on the ground' in Iraq
Testifying to the Senate Armed Services Committee, Carter said the U.S. "won't hold back from supporting capable partners in opportunistic attacks against (ISIS) or conducting such missions directly, whether by strikes from the air or direct action on the ground."
The U.S. has already been conducting special operations forces raids successfully in Iraq and Syria, Michael Stephens, research fellow for Middle East studies at the Royal United Services Institute, told CNN.
Such efforts led to last week's rescue of about 70 hostages from an ISIS prison in Hawija, in northern Iraq, and a raid in al-Omar, Syria, in May in which senior ISIS commander Abu Sayyaf was killed and his wife captured.
The U.S. involvement in Hawija, where special operations forces supporting a Kurdish-led rescue mission were drawn into fighting, was already authorized under the U.S.'s "train and advise" mission in Iraq. Special operations actions such as those carried out in Syria were authorized under counterterror auspices, he said.
Nevertheless, Carter's comments about "conducting such missions directly" point to an escalation in this approach, said Stephens.
The remark, favoring direct action by special operations forces -- even though the Hawija raid resulted in the first American combat death in Iraq since November 2011 -- indicated such raids were viewed by the Pentagon as a successful strategy to degrade the terror group.
"If the U.S. is going to be serious about solving this problem, let's be perfectly honest ... they've got to come in hard," said Stephens.
"Ultimately the policy is already in place to use special forces; the question now is how, and where and in what type of capacity," he said. "My guess is they'll be being used at the front end of supporting other forces on the ground."
There were also questions about how much capacity U.S. special operations forces had to conduct more frequent operations without it taking a toll on morale or personnel, and there were clear limitations to the impact such operations could have, he said.
"You're not going to be able to take a city like Mosul (Iraq's second city, held by ISIS since June 2014) with special forces," he said.
He said it also opened the door to mission creep in the battle against ISIS.
"Will we be going from consistent special forces operations to full army deployments?" he said. "As soon as you're putting guys on the ground on a consistent basis it's not that hard to keep ramping it up."
Raqqa, the Syrian city which is ISIS' stronghold and the capital of its so-called caliphate, is another obvious target in the battle against the terror group.
The city is the headquarters of the "caliphate's" administration and its symbolic heart. It also presents a more achievable target than the much larger Iraqi city of Mosul, said Stephens.
"We've been talking about a liberation of Raqqa for quite a long time now, but as far as I'm concerned there's been almost no progress since ISIS was driven from Kobani," said Stephens.
The effort would require support to Kurdish forces -- who he said were "the most effective force in the area, but not hugely interested in liberating non-Kurdish territory" -- and a rebooted effort to strengthen Syrian moderate forces in the region.
Carter also singled out retaking Ramadi, the predominantly Sunni capital of Iraq's Anbar province, which fell to ISIS in May after more than a year of fighting.
The loss of the strategically and symbolically important city in the country's Sunni heartland just 110 kilometers (70 miles) west of Baghdad "was a huge setback" to the anti-ISIS campaign, said Stephens, and its recapture is critical to defeating the terror group.
"Without taking Ramadi, forget about taking Anbar province, forget about Mosul. You can't defeat the Islamic State unless you take on Ramadi," he said.
The painful defeat in May led to rancor among those engaged in the fight against ISIS, with Carter publicly criticizing the Iraqi army for lacking the will to fight. Driving ISIS from the city by supporting Iraqi security forces with more fire support, as Carter indicated Tuesday, would be a powerful symbolic victory.
Success in Ramadi would also require the Iraqi government to strike the sort of balanced, multisectarian approach that will be needed to beat the terror group across the region. The role of Shiite paramilitary forces in any effort to liberate the city has led to fears of a sectarian bloodbath.
Like Raqqa, Ramadi is a priority because it is a more achievable target than other ISIS-held cities such as Mosul, Iraq's second city.
The shift in approach signaled by Carter's comments would likely have been influenced by the impact of Russia's recent incursion in Syria, which had "changed the realities on the ground," said Stephens.
"The Russians have forced their hand," he said. "While it's encouraging to see the Americans taking a little bit more of the lead, I think they're cognizant of the fact there's been a lot of criticism that the U.S. hasn't been doing enough."