President Barack Obama says there is no easy answer to the problem of rising energy prices, dismissing Republican plans to address the problem as little more than gimmicks.

"We know there's no silver bullet that will bring down gas prices or reduce our dependence on foreign oil overnight," Obama said Saturday in his weekly radio and Internet address. "But what we can do is get our priorities straight and make a sustained, serious effort to tackle this problem."

The people of north Africa's Maghreb region "need and deserve" to determine their own future, U.S. Secretary State Hillary Clinton said in Algeria Saturday, ahead of elections there in May.

Clinton was speaking during a brief visit to the country a day after attending a "Friends of Syria" international gathering in neighboring Tunisia, and hours before flying on to Morocco.

Four people were killed on Friday when anti-U.S. protests turned violent in the western province of Herat, bringing the overall death toll during four days of demonstrations to at least 19, officials said.

Two died as demonstrators surged towards the U.S. consulate in Herat city while two more were killed in Adraskan district, provincial spokesman Moheedin Noori told Agence France Presse.

Seven U.S. Marines were killed when two helicopters collided in Arizona during a training exercise, the military said Thursday.

The accident occurred on a military training range near the city of Yuma on Wednesday evening and the troops who died were from the 3rd Marine Aircraft Wing based at Miramar, in southern California.

Arab and Western powers will challenge the Syrian regime to accept a proposal to allow in humanitarian aid at the "Friends of Syria" meeting in Tunis on Friday, a U.S. official said.

U.S. Secretary of State Hillary Clinton discussed the "unified humanitarian proposal" with counterparts on the sidelines of an international conference on Somalia in London on Thursday, the official said on condition of anonymity.

Several U.S. lawmakers received threatening letters containing a harmless white powder, but the sender warned more missives including a "harmful material" could follow, a Senate official said Wednesday.

The news sparked alarm and served as a grim reminder of the 2001 anthrax attacks in which letters containing the deadly pathogen were sent to offices of two Democratic senators and several media offices. Five people were killed.

France on Wednesday demanded access to the victims of an attack in Syria that killed a U.S. war correspondent and French photojournalist, and summoned Syria's envoy to Paris.

Syria has meanwhile denied that it was aware that the journalists had entered the country.

Australian Prime Minister Julia Gillard said she was "disappointed" the man she deposed as leader, Kevin Rudd, had not discussed plans to resign as Foreign Minister or raised his concerns with her.

Rudd resigned his post at a dramatic midnight press conference in Washington, saying he had lost the confidence of Gillard amid speculation he was preparing a leadership challenge and would return home to consider his future.

Russia on Wednesday said it could not rule out that the United States would use the U.S. Manas airbase in ex-Soviet Kyrgyzstan for an eventual strike on Iran over its contested nuclear program.

"It cannot be excluded that this site could be used in a potential conflict with Iran," foreign ministry spokesman Alexander Lukashevich told reporters. "We hope that such an apocalyptic scenario will not be realized."

Taiwan's navy will arm its submarines with anti-ship missiles for the first time ever beginning next year, a report said Wednesday, as the island boosts its defense capabilities against rival China.

The Taipei-based United Daily News said the navy, which ordered the U.S.-built Harpoon missiles in 2008, recently test-fired the weapons in the United States, in preparation for installing them on its two Dutch-built submarines.