Secretary of State John Kerry, during a visit to Paris in the wake of Friday's Islamic State terror attacks, doubled down on the anti-ISIS strategy and said the U.S. would "increase" its efforts. 

At the same time, he strayed slightly from the Obama administration line that the strategy will remain the same going forward. 

"Obviously there is always room for qualitative improvement," Kerry told Fox News on Tuesday. "The president is always willing to listen. And he said this specifically to everybody. Give me things that work." 

Kerry initially addressed the U.S. strategy in a public statement after meeting with French President Francois Hollande. 

Asked by Fox News whether the administration might change its approach now that ISIS is stepping up attacks and looking beyond the Middle East for targets, Kerry gave a nuanced response. 

While saying there's room for improvement, Kerry ruled out a major contingent of U.S. boots on the ground in Syria, while admitting they could make a "major impact." 

"It didn't work so well in Iraq," he noted.    

He stuck to his line that ISIS' "days are numbered" -- but didn't say how many days. 

"I'm not going to give you a number," he said 

Kerry stressed that the strategy the U.S. is using is "containing" ISIS, from at least a geographic standpoint. He acknowledged that foreign nationals leaving home countries to fight in Syria and then returning remains a problem.   

Ultimately, he said, "I have no doubt that over a period of time Daesh will be defeated." 

Daesh is an alternate name for ISIS.

Greg Palkot currently serves as a London-based senior foreign affairs correspondent for Fox News Channel (FNC). He joined the network in 1998 as a correspondent. Follow him on Twitter@GregPalkot.