Islands at the center of a territorial row between Japan and China are covered by a military protection accord between Washington and Tokyo, U.S. Defense Secretary Chuck Hagel said Monday.

"The United States does not take a position on the ultimate sovereignty of the islands, but we do recognize they are under the administration of Japan and fall under our security treaty obligations," Hagel said at a news conference with his Japanese counterpart Itsunori Onodera.

U.S. President Barack Obama stepped up pressure on Russia over Syria on Monday, telling his Russian counterpart Vladimir Putin of his concern about the reported use of chemical weapons by the Damascus regime.

Obama also thanked Putin in the telephone call for his help after the Boston marathon bombings, and expressed condolences over a fire that killed 36 patients in a Russian psychiatric facility on Friday, the White House said.

Russia on Monday warned the West against using a search for weapons of mass destruction in Syria as an excuse for ousting President Bashar Assad along the lines of the notorious hunt for deadly arms in Saddam Hussein's Iraq.

Russian Foreign Minister Sergei Lavrov questioned why U.N. Secretary General Ban Ki-moon was calling for a fact-finding mission in Syria by citing unproven claims of the regime's use of chemical weapons in December.

Canadian-born former Guantanamo inmate Omar Khadr plans to appeal his conviction for war crimes after two similar cases were quashed, the Toronto Globe and Mail newspaper reported on Saturday.

Khadr, 26, was repatriated to a high-security jail in Canada last September after spending 10 years in the U.S.-run prison following his arrest in Afghanistan as a teenager in 2002.

U.S. authorities said Saturday they have arrested a man as part of a probe into poison-laced letters sent to President Barack Obama and other public officials.

Special agents took James Everett Dutschke into custody "without incident" at his home in Tupelo, Mississippi, around 12:50 Saturday morning, a spokeswoman for the Federal Bureau of Investigation told Agence France Presse.

Syria dismissed as a "barefaced lie" on Saturday American and British claims it may have used chemical arms, as staunch ally Russia warned against using such fears to launch a military intervention in the strife-torn country.

"First of all, I want to confirm that statements by the U.S. secretary of state and British government are inconsistent with reality and a barefaced lie," Syrian Information Minister Omran al-Zohbi said in an interview published on the Kremlin-funded Russia Today's website.

Russian officials blacklisted by the United States over the prison death of lawyer Sergei Magnitsky expressed defiance on Saturday as ministers assured them of the Russian government's support.

The United States this month released a list of 16 Russians allegedly linked to the 2009 death of Magnitsky. They were barred from traveling to the United States or holding assets there in a move that enraged Russia and prompted tit-for-tat measures and a U.S. adoption ban.

An empty soda bottle, crushed charcoal and cola-soaked gauze -- Syrian rebels are scrambling to protect against chemical attacks by regime forces by cobbling together “do it yourself” gas masks from household items.

U.S. President Barack Obama has renewed a warning to Damascus that the use of chemical arms would cross a "red line" as evidence emerged the deadly nerve agent sarin may have been used against the rebels.

A rusted 5-foot-tall piece of landing gear believed to be from one of the hijacked planes destroyed in the Sept. 11 attacks has been discovered near the World Trade Center wedged between a luxury apartment building and a mosque site that once prompted virulent national debate about Islam and free speech.

The twisted metal part, jammed in an 18-inch-wide sliver of open space between the buildings, has cables and levers on it and is about 17 inches wide and 4 feet long, New York Police Department Commissioner Raymond Kelly said Friday.

U.S. President Barack Obama on Friday promised a "vigorous investigation" into reports Syrian forces fired chemical weapons and renewed his warning that proof of their use would be a "game changer."

Obama delivered the warning during talks at the White House with King Abdullah II of Jordan, as he faced rising political pressure for a military intervention in the vicious Syrian civil war.