The United States is doing what it must to "take the fight to terrorists," leading a coalition of Arab nations in a series of airstrikes against the so-called Islamic State terror group in Syria, U.S. President Barack Obama said Tuesday.
At the same time, the United States took action - on its own - against another terrorist organization, the Khorasan Group. Obama described its members as "seasoned al Qaeda operatives in Syria."
U.S. officials said the group was plotting attacks against the United States and other Western targets.
The plots against the United States were discovered by the intelligence community in the past week, an intelligence source with knowledge of the matter told CNN. The source did not say what the target may have been, but said the plot potentially involved a bomb made of a nonmetallic device like a toothpaste container or clothes dipped in explosive material.
A plot involving concealed bombs on airplanes "was just one option they were looking at," a U.S. official said.
"Once again, it must be clear to anyone who would plot against America and try to do Americans harm that we will not tolerate safe havens for terrorists who threaten our people," Obama said in televised remarks from the White House.
Concern over a possible backlash by the terror groups has prompted the U.S. Department of Homeland Security to issue a bulletin warning law enforcement agencies to be on heightened alert for lone-wolf terror attacks on U.S. soil in wake of the airstrikes, a U.S. law enforcement official with knowledge of the warning told CNN.
The bulletin calls for vigilance as well as scrutinizing social media for anyone encouraging violence in response to the strikes, according to a U.S. law enforcement official with knowledge of the warning's contents. It points to the use of social media as a tactic by ISIS to spread its message and call for violence.
It also advises agencies to look for changes in appearance or behavior in those they're tracking, the official said.
See more on this developing story on CNN.com
America's top defense officials left open the possibility of targeting fighters with the so-called Islamic State in Syria, saying during a news briefing Thursday it was not enough to just hit the extremist group in Iraq.
Defense Secretary Chuck Hagel and Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, stopped short of calling for U.S. military action in eastern Syria, an ISIS stronghold.
"Can they be defeated without addressing that part of the organization that resides in Syria? The answer is no," Dempsey said during the briefing at the Pentagon.
Repeatedly pushed by reporters about whether that meant operations against ISIS in Syria, Hagel said, "We're looking at all options."
While it's unclear what those options may be, Hagel said the United States is "very clear-eyed" about ISIS.
"They are beyond just a terrorist group. They marry ideology, a sophistication of strategic and tactical military prowess," Hagel said.
"...This is beyond anything we have seen, and we must prepare for everything. And the only way you do that is that you take a cold, steely hard look at it and get ready."
See more on this developing story on CNN.com
As radical Sunni militants snatch city after city in their march to Baghdad, U.S. Secretary of State John Kerry arrived in Iraq on Monday during the country's tensest time since the U.S. withdrawal of troops.
He'll meet with Prime Minister Nuri al-Maliki, the man some say needs to step down.
With al-Maliki's Shiite-led government losing more ground to militants from the Islamic State in Iraq and Syria (ISIS), Kerry has implored the leader to rise above "sectarian motivations" to become more inclusive and more representative of its population.
Kerry will also meet with Iraq's foreign minister as well as both Shiite and Sunni leaders.
His trip will "emphasize our highest-level commitment to Iraq during this time of crisis," a State Department official said.
Kerry will also speak with key leaders about forming a new government "in line with the constitutional timeline that they're on."
But outside the rooms of high-level talks, parts of Iraq are falling by the day.
See the latest on the crisis that is spilling far beyond Iraq's borders from CNN.com.
Boko Haram launched a grisly attack on a Nigerian village in an area that troops had been using as a base in the search for hundreds of schoolgirls abducted by the militant group, witnesses told CNN on Wednesday.
The hourslong assault on Gamboru Ngala that left at least 150 people dead, some of whom were burned alive, is the latest in a series of brazen attacks and abductions by Boko Haram, raising concern about whether the Nigerian government can retake control of the region from the entrenched terror group.
Word of the attack follows news that President Goodluck Jonathan, who has been under fire for his handling of the mass abduction, accepted U.S., British and Chinese offers of assistance to find the schoolgirls, officials with those governments said.
It's unclear what impact the latest attack could have on the international response to Nigeria's fight with Boko Haram, which so far has concentrated on helping the government rescue 276 schoolgirls abducted on April 14.
The assault on the village came after military troops deployed to the area were called to the border area near Chad, where reports - later determined to be false - surfaced that the schoolgirls had been found with Boko Haram militants, witnesses and local officials said.
CNN cannot independently confirm the report, and attempts Wednesday to contact Nigeria's military for comment were unsuccessful.
We'll have the latest updates on "Early Start."
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The escalating conflict in Ukraine "essentially puts the nation on the brink of civil war," Russian President Vladimir Putin said on Tuesday.
His assessment came during a telephone conversation with his German counterpart, according to the Kremlin, the same day Ukraine's military launched its first, formal military action against pro-Russian militants with troops retaking an airport in the eastern Donetsk region after a reported clash with gunmen.
The military action came a day after a Ukrainian ultimatum expired for protesters to lay down their arms, a move that appeared to signal an escalation in the crisis that has sparked a diplomatic row between Ukraine, its Western allies and Russia.
With pro-Russian militants seizing government and police buildings in as many as 10 towns and cities in eastern Ukraine, acting President Oleksandr Turchynov told Parliament "an anti-terrorist operation" was under way in the region.
The aim of the military operation is to "stop attempts to tear Ukraine to pieces," he told lawmakers.
Witnesses reported hearing gunfire and aircraft that appeared to be coming from the airfield in Kramatorsk, which Turchynov's office said was under the control of Ukrainain special forces late Tuesday.
There were conflicting reports about casualties, with Russian state-run media citing varying casualty claims supplied by militants. According to the reports, there were either two injured or four killed, claims that CNN cannot independently verify.