U.S. and Japanese fighter jets on Tuesday carried out joint air exercises, an official said, days after Chinese and Japanese military planes shadowed each other near disputed islands in the East China Sea.

The five-day exercise involves six U.S. FA-18 fighters and around 90 American personnel, along with four Japanese F-4 jets and an unspecified number of people, the official said.

Iran is on track to be able to produce material for at least one nuclear bomb by mid-2014 as sanctions hit its economy but fail to stop the atomic program, a U.S. think tank said Monday.

The Institute for Science and International Security, a private group opposed to nuclear proliferation, called for tougher U.S. economic sanctions against Iran and pressure on major trading partners to isolate Tehran.

President Barack Obama warned of a new economic crisis Monday and said global stock markets would go "haywire" unless Republicans in Congress agree to raise the U.S. sovereign debt ceiling.

"To even entertain the idea of this happening, of the United States of America not paying its bills, it is irresponsible, it is absurd," Obama said in repeating his demand for a debt limit rise.

The president of the top U.S. firearms lobby said Sunday that his organization has enough backing from lawmakers to defeat a plan to outlaw assault weapons and sales of high-capacity ammunition clips.

David Keene, president of the National Rifle Association, told CNN's "State of the Union," such proposals will not pass, despite recent widespread outrage at the shooting deaths of 26 pupils and staff at a Connecticut school.

U.N.-Arab League peace envoy Lakhdar Brahimi on Friday expressed the urgent need to end the Syrian conflict after meeting with top U.S. and Russian officials, but reported no concrete advances towards a solution.

"We all stressed the need for a speedy end to the bloodshed and the destruction and all forms of violence in Syria," Brahimi told reporters in Geneva, following more than five hours of talks with Russian Deputy Foreign Minister Mikhail Bogdanov and U.S. Deputy Secretary of State William Burns.

Russian children whose adoption has already been approved by the courts will be able to go to the United States despite a blanket ban on American adoptions, a Kremlin spokesman said on Friday.

"Those who have received a court decision will go," President Vladimir Putin's spokesman Dmitry Peskov told AFP.

U.N.-Arab League peace envoy Lakhdar Brahimi was meeting with top U.S. and Russian officials Friday on the Syria crisis although there was little hope of a breakthrough.

Brahimi, Russian Deputy Foreign Minister Mikhail Bogdanov and U.S. Undersecretary of State William Burns were meeting at the U.N. headquarters in Geneva. They made no comment as they arrived for the closed-door talks.

The United States sought to assure Afghan President Hamid Karzai on Thursday that it would remain committed to his country even as U.S. officials weigh a major withdrawal of American forces.

After an elaborate military ceremony for Karzai outside the Pentagon, U.S. Defense Secretary Leon Panetta told his "distinguished visitor" that more than 10 years of war had paved the way for Afghanistan to stand on its own.

President Barack Obama picked Jack Lew as his new Treasury secretary Thursday and called on the Senate to confirm him as quickly as possible, so he can press on with the work of reviving the economy.

Lew, Obama's current chief of staff, is slated to take over from Tim Geithner, who stood by Obama's side at the darkest moments of the crisis that was hammering American jobs and prosperity when he took office in 2009.

U.S. Vice President Joe Biden said he would get the results of his probe into curbing gun violence to President Barack Obama by Tuesday, as the response to the Newtown school massacre gathers pace.

As he met officials from sporting and hunting groups Thursday, Biden hinted that his ideas could include new restrictions on the use of high capacity ammunition magazines and more comprehensive background checks for gun buyers.