The United States and Turkey on Thursday signed a deal to train and equip Syrian rebel forces, officials said.

"Turkey and the United States signed a document a short time ago on the train-and-equip (program)," Turkish Foreign Minister Mevlut Cavusoglu told reporters.

Army Commander General Jean Qahwaji headed to the Saudi capital Riyadh to take part in a two-day meeting for military leaders from more than 20 partner nations in a U.S.-led coalition to degrade and destroy Islamic State of Iraq and the Levant (ISIL).

Qahwaji traveled on Wednesday night to Saudi Arabia.

The United States will provide basic military training and equipment to Syrian rebels and may eventually instruct them on how to call in air strikes against Islamic State jihadists, the Pentagon said Wednesday.

But for the moment, the training will focus on fundamentals and not the more complicated task of directing U.S.-led warplanes to a particular target, the skilled job of a forward air controller, Pentagon spokesman Rear Admiral John Kirby told reporters.

President Barack Obama said the fight against violent extremism is a "battle for hearts and minds," as he called for unity on the second day of a conference bringing together 60 countries Wednesday.

Stressing that the fight against groups like Islamic State cannot be won with military might alone, Obama is expected to talk about "discrediting the voices of extremism" within communities and across the world.

A U.S. diplomat underestimated Lebanon's decision to boycott a conference expected to be held in Washington after Beirut claimed that it cannot take part in a meeting to confront terrorism with the Jewish state's participation.

“Cooperation between the Lebanese and U.S. security agencies is ongoing,” the diplomatic source said in comments published in al-Liwaa newspaper on Wednesday.

The United States said Tuesday that it will allow for the first time the widespread export of armed drones to some allied countries as part of its global counterterrorism fight.

Armed drones are a cornerstone of Washington's battle against extremists in Afghanistan, Pakistan, Somalia, Syria, Iraq and Yemen, although they remain hugely controversial and opponents say they frequently kill or maim civilians.

Islamist group Boko Haram has vowed to make voting impossible in Nigeria's upcoming election after a spate of deadly attacks in the country's violence-wracked northeast.

The group's leader Abubakar Shekau said in a new video posted on Twitter late on Tuesday evening that his fighters would disrupt polling in Africa's most populous nation scheduled for March 28.

The United States and Turkey have agreed "in principle" on a deal to train and equip Syrian rebel forces, the State Department said Tuesday.

"As we have announced before, Turkey has agreed to be one of the regional hosts for the train-and-equip program for moderate Syrian opposition forces," department spokeswoman Jen Psaki told reporters. 

Ashton Carter was sworn as the new U.S. defense secretary on Tuesday and pledged that he and the top brass would give President Barack Obama their "candid" advice on matters of war and peace.

Carter took the oath of office in a ceremony presided over by Vice President Joe Biden, who said the Pentagon chief faced the task of ensuring the American military remained "second to none" and that the government meet its "sacred obligation" to take care of those who volunteer for the armed forces.

Reeling from a string of bloody terror attacks from Denmark to Libya, representatives from 60 countries will gather from Tuesday for a White House summit on combating violent extremism.

The three-day meeting hosted by President Barack Obama has been in the pipeline for months, but has been given deeper significance in the wake of several similarly inspired attacks.