Speaking at the Washington-based think tank Center for Strategic and International Studies, the director of the US Central Intelligence Agency (CIA), John Brennan, said Monday that "Islamic State" plans for operations similar to Friday's attacks in Paris were "inevitable."

"I would anticipate that this is not the only operation ISIL has in the pipeline," Brennan said, referring to the Islamic State militant group by an alternate acronym to "IS."

"This was not something done in a matter of days. This is something that was carefully and deliberately planned over the course of several months in terms of whether they had the operatives, the weapons, explosives, suicide belts."

The CIA chief added that since the Paris attacks, intelligence agencies have exerted significant efforts to curb the militant group's ability to conduct another attack.

"Security and intelligence services right now are working feverishly to see what else they can do in terms of uncovering," Brennan added.

Closing the door?

Friday's attacks have raised fears among Europeans and Americans that a wave of migrants and refugees fleeing war-torn countries in the Middle East, Asia and Africa may have provided Islamic State militants an opportunity to enter the US and EU.

Two US states have announced that they will be suspending a federal resettlement program of Syrian refugees following Friday's attacks.

"After full consideration of this weekend's attacks of terror on innocent citizens in Paris, I will oppose any attempt to relocate Syrian refugees to Alabama through the US Refugee Admissions Program," said Alabama Governor Robert Bentley.

Michigan Governor Rick Snyder echoed Bentley's sentiments, saying that the northern state would not accept "new refugees until the US Department of Homeland Security completes a full review of security clearance and procedures."

Republican Senator Rand Paul said he would introduce a bill to Congress that would enact an immediate moratorium on US visas for refugees fleeing violence in about 30 countries affected by militant groups.

'Cannot close our doors to these people'

However, State Department spokesman Mark Toner said that the US will continue with its plans to resettle 10,000 Syrian refugees in the coming months, as experts said states lack the legal authority to curb the resettlement program.

"These refugees are subject to the highest level security checks of any category of traveler to the United States," Toner told a press briefing.

"We think we can do this safely and in a way that reflects American values," Toner added.

In Paris, US Secretary of State John Kerry said America will continue to accept those fleeing militant violence.

US President Barack Obama's deputy national security adviser, Ben Rhodes, said that there is little risk for states resettling Syrian refugees due to the country's "robust" vetting process.

"We cannot close our doors to these people," Rhodes told the Fox News Sunday program, AFP news agency reported.

ls/kms (AP, AFP)