Americans on Thursday marked the 13th anniversary of the September 11, 2001 attacks, with somber ceremonies of remembrance in New York and Washington.

President Barack Obama, his wife Michelle and Vice President Joe Biden observed a moment of silence on the White House south lawn, along with about 300 staffers. Flags in Washington flew at half-mast. 

Iraqi Prime Minister Haidar al-Abadi welcomes U.S. President Barack Obama's strategy of air strikes and support for Baghdad's forces to defeat the Islamic State (IS) jihadist group, his office said Thursday.

"Iraq welcomes Obama's strategy about standing with it in its war against (IS) and the terrorist groups," the statement from Abadi's office said.

Syria's opposition National Coalition welcomed a U.S. plan to tackle the jihadist Islamic State group on Wednesday, but also urged action against President Bashar Assad's regime.

In a statement, the group said it backed a U.S. plan for air strikes in Syria and training of rebel forces, but that a "stable and extremist-free region" required "degrading and ultimately removing the Assad repressive regime."

Hizbullah deputy chief Sheikh Naim Qassem considered on Thursday that the United States inwardly accepts the presence of the Islamic State of Iraq and the Levant in the region.

“They are trying to prevent it from reaching its states but they don't want it to end,” Qassem said in comments published in As Safir newspaper.

Opening a new military front in the Middle East, President Barack Obama authorized U.S. airstrikes inside Syria for the first time Wednesday night, along with expanded strikes in Iraq as part of "a steady, relentless effort" to root out Islamic State extremists and their spreading reign of terror.

"We will hunt down terrorists who threaten our country, wherever they are," Obama declared in a prime-time address to the nation from the White House. "This is a core principle of my presidency: If you threaten America, you will find no safe haven."

He spent eight years bending the ear of George W. Bush. On Wednesday, former vice president Dick Cheney sought to advise another U.S. leader, this time over how to contend with violent jihadists.

In a Washington speech, Cheney, an architect of the U.S. invasion of Iraq in 2003, criticized a "disengaged" President Barack Obama for his defensive posture in the face of extremist threats, including those posed by the Islamic State (IS).

U.S. President Barack Obama spoke by phone with Saudi King Abdullah on Wednesday and met his top national security and intelligence advisors ahead of his prime time speech on the Islamic State.

Obama called Abdullah from the Oval Office, underlining Saudi Arabia's role as a potentially key member of the international coalition Obama is trying to build to take on the jihadist group.

Foreign Minister Jebran Bassil is scheduled to travel to Jeddah to attend talks on joint action against the Islamic State (IS) group, a cabinet minister said.

The minister, who was not identified, told al-Liwaa newspaper published Wednesday that Bassil will attend a meeting between U.S. Secretary of State John Kerry and around nine Arab states in addition to Turkey.

U.S. lawmakers slammed President Barack Obama Tuesday for failing to notify Congress before releasing five Taliban operatives from Guantanamo in exchange for an American POW.

U.S. officials, fearing for the life and health of U.S. Army Sergeant Bowe Bergdahl who had been held captive for five years, swiftly negotiated for his release in a controversial May swap that fueled a major political dust-up in Washington, as critics accused Obama of sidestepping Congress.

President Barack Obama's upcoming visit to China will be an "important milestone" in relations, the top White House national security aide said Monday at a meeting with officials in Beijing.

The trip by National Security Advisor Susan Rice comes at a turbulent time in U.S. foreign policy and some three weeks after Washington accused a Chinese fighter jet of buzzing one of its surveillance planes.