The first punishing wave of US missiles in Syria targeted an al-Qaeda terror cell that was “nearing the execution phase’’ of a plot to sneak explosives onto a plane in America or Europe, officials said Tuesday.

The mysterious Khorasan Group is believed to have been devising a nonmetallic bomb that could get past airport metal detectors by being hidden in a toothpaste container or in clothes dipped in explosives, sources told CNN.

The plot was only discovered in the past week, the sources 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,’’ President Obama said at the White House before heading to the United Nations, where he is expected to address the war on ISIS Wednesday.

Arab support for the airstrikes “makes it clear to the world this is not America’s fight alone,” Obama said, referring to the five Arab countries that participated in the attack.

US officials said the military campaign will be long and relentless.

“I can tell you that last night’s strikes were only the beginning,’’ Rear Adm. John Kirby said.

The Pentagon released video and photos of targeted sites before and after the attacks — showing many reduced to rubble.

There were three waves of airstrikes Monday — the first involving only US warplanes and mainly targeting training camps of the Khorasan Group, explosives warehouses and communications and other control centers in eastern and northern Syria.

In total, U.S. Central Command conducted eight strikes against Khorasan Group targets west of Aleppo to include training camps, an explosives and munitions production facility, a communication building and command and control facilities.

The Khorasan Group had been focused on recruiting and training American and European extremists with passports for its bomb plots, authorities said. It had recently been testing bombs in Syria.

“The Khorasan Group is clearly not focused on either the Assad regime or the Syrian people,” said Lt. Gen. William Mayville, director of operations for the Joint Chiefs of Staff. “They are establishing roots in Syria in order to advance attacks against the West and the homeland.”

Two more strikes — this time with the help of aircraft from the Arab allies — targeted ISIS’s headquarters, training camps and combat vehicles, officials said.

ISIS has executed two US journalists and a British aid worker in horrific beheadings it claimed were payback for US airstrikes against it in Iraq.

In response to Monday’s attack against them in Syria, ISIS thugs released a new online video in which British hostage John Cantlie was forced — for the second time in less than a week — to act as their mouthpiece.

The coerced, haggard-looking Cantlie said the US had just started “Gulf War III,’’ adding, “Not since Vietnam have we witnessed such a potential mess in the making.”

Outside Baghdad on Tuesday, ISIS members also paraded exhausted-looking captured Iraqi soldiers through the streets.

“It is not just about warheads on foreheads,” Kirby said of the United States’ attempt to bring both terror groups to their knees. “It is about degrading the capability to operate, command and control.”

B-1 bombers, F-16, F-18 and F-22 Raptor stealth fighters and drones were among the warplanes deployed to nail 22 sites, firing off a total of 200 missiles.

Among the areas targeted were Raqqa, an ISIS stronghold, and around Syria’s largest city, Aleppo.

Some missiles were fired from the USS Arleigh Burke in the Red Sea, as well as from the USS Philippine Sea and the USS George H.W. Bush in the northern Persian Gulf, authorities said. Others came from aircraft that took off from undisclosed bases in the area.

Recep Tayyip Erdogan, the president of Turkey, a NATO member, suggested on Tuesday that his country would soon participate, too.

“We will give the necessary support to the operation. The support could be military or logistics,’’ he said.

The Syrian Observatory for Human Rights reported up to 70 militants dead and another 300 wounded in the attacks.

The al-Qaeda offshoot al-Nusra Front said its leader, Abu Yousef al-Turki, was among those killed.

The Syrian human-rights group said at least eight civilians, including three children, also died in the assault. None of those figures could be immediately confirmed.

“We warned Syria not to engage US aircraft. We did not request the [Syrian] regime’s permission,’’ said State Department spokeswoman Jen Psaki.

In a related development, the wife of British hostage Alan Henning said she received an audio recording of her husband being held by ISIS and pleading for his life.

ISIS previously posted photos of Alan Henning dressed in orange clothes and kneeling before a black-clad fiend holding a knife.