(AP) -- The U.S. and partner nations began launching airstrikes against Islamic State group targets in Syria for the first time Monday night, expanding a military campaign against the militants with a mix of fighter jets, bombers and Tomahawk cruise missiles fired from ships in the region.

The strikes were part of the expanded military campaign that President Barack Obama's authorized nearly two weeks ago in order to disrupt and destroy the Islamic State militants, who have slaughtered thousands of people, beheaded Westerners, including two American journalists, and captured a large swath of territory stretching from within Syria to land across northern and western Iraq.

Because the military operation was ongoing, no details could be provided yet, said Rear Adm. John Kirby, the Pentagon's press secretary. He said the decision to strike was made earlier Monday by the military. He did not name the partner nations participating in the operation; however U.S. officials have said the U.S. would not launch this mission alone and some Arab nations had been expected to participate.

Some of the airstrikes of airstrikes were against Islamic State group targets in Raqqa. Military officials have said the U.S. would target militants' command and control centers, re-supply facilities, training camps and other key logistical sites.

"We will be prepared to strike ISIL targets in Syria that degrade ISIL's capabilities," Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told senators last week, using one of the acronyms for the Islamic State group. "This won't look like a shock-and-awe campaign, because that's simply not how ISIL is organized, but it will be a persistent and sustainable campaign.

Defense Secretary Chuck Hagel said that the plan "includes targeted actions against ISIL safe havens in Syria, including its command and control logistics capabilities and infrastructure." He said he and Dempsey approved the plan.

The U.S. has also been increasing its surveillance flights over Syria, getting better intelligent on potential targets and militant movements.

Military leaders have said about two-thirds of the estimated 31,000 Islamic State militants were in Syria.

In a speech Sept. 10, Obama vowed to go after the Islamic State militants wherever they may be. And his military and defense leaders told Congress last week that airstrikes within Syria are meant to disrupt the group's momentum and provide time for the U.S. and allies to train and equip moderate Syrian rebels.

The U.S. military has been launching targeted airstrikes in Iraq since August, focusing specifically on attacks to protect U.S. interests and personnel, assist Iraqi refugees and secure critical infrastructure. Last week, as part of the newly expanded campaign, the U.S. began going after militant targets across Iraq, including enemy fighters, outposts, equipment and weapons.

To date U.S. fighter aircraft, bombers and drones have launched about 190 airstrikes within Iraq.

Urged on by the White House and U.S. defense and military officials, Congress passed legislation late last week authorizing the military to arm and train moderate Syrian rebels. Obama signed the bill into law Friday, providing $500 million for the U.S. to train about 5,000 rebels over the next year.

U.S. leaders have also been crisscrossing the globe trying to build a broad international coalition of nations, including Arab countries, to go after the Islamic State group and help train and equip the Iraqi security forces and the Syrian rebels.

The militant group, meanwhile, has threatened retribution. Its spokesman, Abu Mohammed al-Adnani, said in a 42-minute audio statement released Sunday that the fighters were ready to battle the U.S.-led military coalition and called for attacks at home and abroad.