CIA chief David Petraeus met Turkey's Prime Minister Recep Tayyip Erdogan on Tuesday for closed-door talks focusing on the crisis across the border in Syria.

Petraeus, director of the U.S. Central Intelligence Agency, also discussed the latest developments in neighboring Iran and efforts to counter Kurdish rebels attacking Turkey from safe havens in northern Iraq, said NTV television channel.

Kyrgyzstan on Tuesday warned visiting U.S. Defense Secretary Leon Panetta that American forces could not use a strategic air base for any military mission after the current lease expires in 2014.

The Manas air base at Bishkek airport serves as a crucial hub for the NATO-led force in Afghanistan and U.S. officials are concerned about the future of Manas as they review plans for troop deployments beyond mid-2014.

U.S. Secretary of State Hillary Clinton on Tuesday vowed to press ahead with support for democracy promotion groups, saying that they play a critical role despite a crackdown in Egypt.

Clinton, addressing U.S. ambassadors from around the world who are back in Washington for a group conference, said that civil society groups are vital to encouraging U.S. goals such as advancing democracy and women's participation.

Russia said Tuesday it will press Syria to accept international monitors who could observe the implementation of a "simultaneous" ceasefire between government troops and rebels.

Foreign Minister Sergei Lavrov said Russia was discussing the proposal with both the Arab League countries and at the United Nations, where the Security Council debated the crisis on Monday.

The U.S. soldier suspected of killing 16 Afghan civilians in a shooting rampage could face the death penalty if convicted, U.S. Defense Secretary Leon Panetta said Monday.

The Pentagon chief told reporters aboard his plane en route to Kyrgyzstan that the suspect in the Afghan shooting spree would be brought to justice under the U.S. military legal code, which allows for the death penalty in some cases.

A University of Maryland student was arrested and taken for psychiatric evaluation after posting threats about a shooting rampage that would "make it to the national news," the school said.

The university's Department of Public Safety said it made the arrest Sunday of Alexander Song, 19, after learning of the threats at the university's campus at College Park, Maryland.

The Afghan parliament demanded Monday that a U.S. soldier who went on a shooting spree and killed 16 villagers in their homes should be put on public trial in Afghanistan.

"We seriously demand and expect that the government of the United States punish the culprits and try them in a public trial before the people of Afghanistan," the lower house of parliament said in statement.

Top officials from the United States, Russia, United Nations and European Union will meet Monday to discuss deadlocked efforts to end the Israel-Palestinian conflict, the U.N. said.

It will be the first top level meeting of the diplomatic Quartet in six months and comes amid a new flare-up in violence which has left at least 21 Palestinians dead in Israeli raids on the Gaza Strip since Friday.

Iran stands fully behind Syria and blames the United States and Arab nations for the bloody unrest shaking its ally, media on Monday quoted a deputy foreign minister as saying.

"The Islamic Republic of Iran underlines its total support for the Syrian people and government," Hossein Amir Abdollahian said, according to Iran's official IRNA news agency.

The U.S. commander of the NATO-led force in Afghanistan promised a "rapid and thorough investigation" into a killing spree by a U.S. soldier that claimed 16 lives, including nine children.

"I am absolutely dedicated to making sure that anyone who is found to have committed wrong-doing is held fully accountable," General John Allen, the commander of the International Security Assistance Force, said.