Defense Secretary Chuck Hagel on Thursday criticized changes made by U.S. lawmakers to last year's defense budget as purely political and contrary to the department's future as envisioned by Pentagon leaders.

Hagel expressed frustration that -- despite Pentagon efforts to trim programs it deems bloated -- members of Congress have reintroduced expendable programs, apparently to please constituents in their home districts.

The U.S. Senate voted Thursday to debate the most ambitious gun safety legislation in nearly two decades, after a bipartisan group of lawmakers agreed on expanding background checks for firearm sales.

With relatives of the 20 children killed in the Newtown massacre watching from the visitors' galleries, lawmakers overcame Republican obstruction and overturned years of Senate refusal to address the nation's gun laws.

Britain has invited all the surviving U.S. ex-presidents to the funeral of former premier Margaret Thatcher next week as part of a more than 2,000-strong guest list, Prime Minister David Cameron's office said on Thursday.

All of Britain's surviving ex-prime ministers have also been invited along with a representative of the family of South Africa's Nelson Mandela and representatives from around 200 states and international organisations, Downing Street said in a statement.

The United States on Wednesday led a boycott of a U.N. meeting where Serbia's President Tomislav Nikolic launched a fierce attack on international war crimes tribunals.

The U.S. mission condemned the meeting organized by the head of the U.N. General Assembly, Serbia's Vuk Jeremic, as "unbalanced" and "inflammatory."

North Korea is "skating very close to a dangerous line" with its heated rhetoric and provocative actions, U.S. Defense Secretary Chuck Hagel told reporters Wednesday.

The United States and its allies hoped Pyongyang would tone down its inflammatory language but the American military was prepared for any possibility, Hagel said.

The United States reacted with concern Wednesday after Iran unveiled a new uranium production facility and two extraction mines, but said it had not been "blindsided" by the news.

Iranian President Mahmoud Ahmadinejad hailed the advances on Tuesday and boasted of mastery over "the entire chain of nuclear energy" only days after talks with world powers on its disputed nuclear program ended in deadlock.

The United States is mulling ways to step up support for the Syrian opposition, a top U.S. official said Wednesday, as U.S. Secretary of State John Kerry and G8 ministers were to meet rebel leaders.

"The United States every single day thinks about what more we can do to help bring this horrible situation to an end," the senior U.S. administration official said, asking not to be identified.

South Korea raised its military watch alert to "vital threat" Wednesday before an expected North Korean missile launch, as U.N. chief Ban Ki-moon warned the Korean peninsula may be slipping out of control.

The North last week, told foreign diplomats in Pyongyang they had until April 10 to consider evacuation, fueling speculation a launch was planned between Wednesday and the April 15 birthday celebrations for late founder Kim Il-Sung.

A top U.S. military commander said Tuesday he favored shooting down a North Korean missile only if it threatened the United States or Washington's allies in the region.

When asked by lawmakers if he supported knocking out any missile fired by North Korea, Admiral Samuel Locklear, head of U.S. Pacific Command, said: "I would not recommend that."

U.S. Secretary of State John Kerry on Tuesday said he would meet representatives of the Syrian opposition in London, speaking shortly before taking off from Israel for the British capital.

"I will be meeting with the Syrian opposition in London," he told reporters before departing from Ben Gurion airport near Tel Aviv after three days of talks with Israeli and Palestinian leaders.