The United States has delivered an emergency shipment of weapons to Lebanon's military, officials said Friday, part of a broader regional effort to combat the growing threat posed by Islamic extremists.

The Lebanese government requested the weapons after militants from Syria attacked the Lebanese border town of Arsal earlier this month, killing and kidnapping soldiers and police in the most serious spillover of violence into the tiny country from the neighboring civil war.

Photographs surfaced online Friday purporting to show the beheading of a Lebanese soldier who was seized during the Arsal incursion. The pictures were posted on a militant website and on Twitter by supporters of the Islamic State extremist group, but have not been confirmed by the Lebanese army.

The new weapons were displayed at a Beirut air base on Friday after arriving overnight. A sample of the weapons -- mortars, M16-A4 assault rifles and anti-tank missiles -- were placed on a white satin-covered table with camouflage netting.

"This is just the latest in a series of deliveries that have arrived in the last 36 hours," U.S. ambassador David Hale said at the event. Hale said the U.S. had so far delivered 480 anti-tank guided missiles, over 1,500 M16-A4 rifles, and mortars. "More mortars, grenade launchers, machine guns, and anti-tank weapons will be arriving," he said.

After Hale spoke, a U.S. military aircraft that landed at the air base was opened to reveal wooden boxes full of weaponry. "This aircraft is full, chock-full!" said Antonio Banchs, defense attache to the U.S. embassy, as he surveyed the goods.

The weapons shipment is part of a region-wide response -- which is still taking shape -- to the rapid advances of the Islamic State extremist group, which has seized vast swaths of Syria and Iraq and threatens several U.S. allies.

The U.S. has said it would bolster Kurdish forces with new weapons as they try to fend off advances by the Islamic State militants into their largely-autonomous region of northern Iraq. The U.S. is also now conducting airstrikes to push back the extremists in northern and western Iraq, its first direct military involvement in the country since troops withdrew at the end of 2011.

The U.S. is also mulling airstrikes in Syria, after long refusing to intervene in the three-year-old conflict, which is now a complex civil war.

Lebanese Interior Minister Nohad Machnouk warned Thursday that Arsal was still a "time-bomb ready to explode anytime."

Before retreating earlier this month toward Syrian territory, the militants, including fighters of the Islamic State group, took with them some 28 captured Lebanese soldiers and police.

On Friday, they posted photos purporting to show one of them, Sergeant Ali Sayid, beheaded

The photos sparked a protest in northern Lebanon by families of the kidnapped soldiers.

Weeks earlier, a video of Sayid emerged in which he announced his defection from the Lebanese army to join the ranks of the Islamic State group. However, he appeared to have spoken under duress.

The Islamic State group has used violence, and images of violence, to strike fear into their rivals.

The Lebanese army had no comment, saying it was still investigating the photographs.