The world's top diplomats pledged Monday to support Iraq in its fight against Islamic State militants by "any means necessary," including "appropriate military assistance," as leaders stressed the urgency of the crisis.

Representatives from around 30 countries and international organizations, including the United States, Russia and China, gathered in Paris as the brutal beheading over the weekend of a third Western hostage focused participants' minds.

An alleged German jihadist went on trial Monday accused of fighting in Syria for the Islamic State group, amid calls for tougher action to prevent attacks in Europe by militants.

In the first German criminal proceedings involving IS, Kreshnik Berisha, a 20-year-old born near the business capital Frankfurt to a family from Kosovo, has been charged with membership of a foreign terrorist organization.

Interior Minister Nouhad al-Mashnouq warned on Monday of the dangerous situation in the northeastern border town of Arsal with the onset of winter as gunmen would have to leave their positions on the outskirts either back into Syria or would enter the village.

“If the jihadists decided to advance into Arsal at the beginning of winter new clashes would erupt with the Lebanese army,” Mashnouq said in an interview with the pan-Arab daily Asharq al-Awsat.

French planes carried out their first reconnaissance flights over Iraq on Monday in support of the U.S.-led campaign against Islamic State jihadists.

An AFP correspondent saw two French Rafale fighter jets equipped with high-precision cameras take off from the Al-Dhafra base in the United Arab Emirates during a visit by French Defense Minister Jean-Yves Le Drian.

Security forces are questioning several suspects who were arrested in the southern district of Jezzine on suspicion of plotting to free Islamist prisoners loyal to Salafist cleric Sheikh Ahmed al-Asir, al-Akhbar newspaper reported on Monday.

The daily said that the cell was planning to attack the Jezzine prison to free the inmates who were arrested during and after clashes between gunmen loyal to al-Asir and the Lebanese army in June 2013.

A Qatari delegation is expected to arrive on Tuesday in Lebanon after a short one-day visit to Doha by a Lebanese delegation headed by Prime Minister Tammam Salam.

The delegation, according to An Nahar newspaper, is set to follow up the case of the Lebanese soldiers and policemen abducted by jihadists.

The U.N. Security Council on Sunday condemned the "heinous and cowardly murder" of British aid worker David Haines by an Islamic State militant.

"This crime is a tragic reminder of the increasing dangers humanitarian personnel face every day in Syria," the council emphasized in a statement, adopted unanimously by its 15 members.

The head of the main Syrian opposition group in exile said Sunday he expected the support of the international community to press the fight against Damascus and Islamic State jihadists.

The United States is pushing for the formation of a broad international coalition to tackle IS which has captured swathes of Iraq and Syria, and has already secured the backing of 10 Arab states including Saudi Arabia.

Success of the U.S. campaign against Islamic State militants will come when the group no longer poses a threat to the United States and its allies in the Middle East, a top U.S. official said Sunday.

U.S. national security advisor Denis McDonough appeared to calibrate President Barack Obama's vow to "degrade and ultimately destroy" the militant group, in spelling out U.S. objectives in an interview with NBC's Meet the Press.

The United States will not coordinate air attacks on Islamic State militants with Syria but will seek to ensure their forces do not come into conflict, U.S. Secretary of State John Kerry said in an interview aired Sunday.

"We will certainly want to deconflict and make certain that they're (Syria) not about to do something that they might regret even more seriously," Kerry said in the interview on CBS's Face the Nation.