The Obama administration drew fire Thursday from a growing list of frustrated lawmakers over the release of more Guantanamo detainees -- this time Yemeni terrorists to the volatile Arabian Peninsula -- as concerns mount over the spreading threat of Islamic terrorism, and the administration's refusal to publicly call out Islam's radical elements. 

The Department of Defense announced Wednesday that five Yemeni terror suspects held at Guantanamo Bay were released -- with four of the five heading for Oman, Yemen's neighbor. 

The release comes despite knowledge that one of the two assassins who carried out the Charlie Hebdo massacre in Paris traveled to Yemen in 2011, and met with the radical American cleric Anwar al-Awlaki. 

"The administration continues to transfer Guantanamo detainees while providing virtually no details to the American people regarding the risk the detainees present to our country and our allies, as well as the detainees' affiliations with terrorist groups and the conditions of their transfer," Sen. Lindsey Graham, R-S.C., Sen. Kelly Ayotte, R-N.H., and Sen. John McCain, R-Ariz., said in a statement on the releases. 

They also cited reports that Oman may have been the entry point for the Paris attacker who traveled to Yemen. "We just sent four Guantanamo detainees, with potential ties to al Qaeda, to Oman -- the same country that reportedly served as the jumping off point" for that travel, they said. 

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Amid the drive to release Guantanamo prisoners, more evidence is mounting that Islamic terrorism is spreading around the world -- including a claim of responsibility by Al Qaeda in Yemen for the Paris terror attacks, and the unchecked slaughter of thousands in Nigeria by Boko Haram. Police in Belgium also claimed Thursday to have stopped a "Belgian Charlie Hebdo," with government agents killing at least two in raids aimed at jihadists returning from Syria who were planning to launch terrorist attacks. 

The administration is taking heat not only for the Gitmo transfers, but for its refusal to publicly call out radical Islam as the common thread in these attacks. 

"The president of the United States has concluded that the War on Terror has reached a point that we can safely release people from Gitmo," Graham told Fox News on Wednesday. "The best I can say about him is he's unfocused. That's delusional thinking. The War on Terror has reached a lethal phase, and it is insane to be letting these people out of Gitmo to go back to the fight." 

The Defense Department stresses that most detainees released under this administration "live quietly" in locations around the world. Asked about the latest transfers to Oman, a Defense spokesman said such a decision is only made after "detailed, specific conversations with the receiving country about the potential threat a detainee may pose after transfer and the measures the receiving country will take in order to sufficiently mitigate that threat.

"If we do not receive adequate security and humane treatment assurances, the transfer does not occur," the spokesman said.

Though Al Qaeda in the Arabian Peninsula and militants in that region are asserting themselves once again as a global threat, other Islamist groups and self-radicalized operatives are posing grave security risks to dozens of countries. In Iraq and Syria, the Islamic State continues to hold ground in its war against the governments there and its quest for its own nation state. 

In Nigeria, the terror group Boko Haram has seized territory said to be the size of the Islamic State's, while committing mass murders against the civilian population. Earlier this month, as many as 2,000 people were slaughtered by the terror group, rights groups say. 

The Paris terror attack and the raid in Belgium were reminders of the threat from cells in Western Europe. 

But other recent plots and attacks by lone-wolf types have occurred in Canada, Australia and the United States. An alleged sympathizer of the Islamic State terror group was arrested in Ohio on Wednesday after authorities learned that he was plotting a shooting and bombing attack on the U.S. Capitol. 

Yet the administration has been loath to term the problem as radical Islam. 

White House Press Secretary Josh Earnest explained that, in their view, "these terrorists are individuals who would like to cloak themselves in the veil of a particular religion." 

He added, "But based on the fact that the religious leaders of that religion have roundly condemned their actions, those religious leaders have indicated that their actions are entirely inconsistent with Islam." 

Earnest said he wouldn't criticize anybody who does use that label. 

This would include the French government, whose ambassador to the U.S., Gérard Araud, told Fox News on Wednesday that "we are at war with radical Islam." 

Graham, also speaking on Fox News, said that "when our president doesn't acknowledge this is a religious-driven war, it's going to be very hard to win it." 

Meanwhile, four of the latest Guantanamo transfers will be going to Oman, and one will be going to Estonia. 

In a statement, the Defense Department said the transfers were "unanimously approved" by all agencies responsible for reviewing them. 

"The United States coordinated with the Government of Oman to ensure these transfers took place consistent with appropriate security and humane treatment measures," the DOD said. 

Several Republican senators including Ayotte have introduced legislation to clamp down on Obama's ability to transfer terror suspects out of the detention facility. These senators called for a "time out" on releasing more detainees after the Paris terror attacks. 

The bill would prohibit transfers of terror suspects to foreign countries if there has been a confirmed case where an individual was transferred from Guantanamo and engaged in any terrorist activity. Any transfers to Yemen would be shut down for two years. 

The Associated Press contributed to this report.