WASHINGTON – The US seeks to destroy the metastasizing Islamic State, President Barack Obama said from Eastern Europe on Wednesday, reacting angrily to the murder of a second American citizen at its hands in two weeks.

The killers of journalists James Foley and Steven Sotloff taking refuge in Syria will be held accountable, “no matter how long it takes,” US Secretary of State John Kerry echoed from Washington, calling Sotloff’s murder an act of evil.

The public comments from both Kerry and Obama suggest the scope of America’s mission against Islamic State, the terrorist Islamist group, has now been broadened, as the president warned that his objective is no longer limited to the protection of US assets and personnel in the Iraqi cities of Arbil and Baghdad.

“Our objective is clear, and that is to degrade and destroy ISIL [Islamic State] so that it’s no longer a threat, not just to Iraq but also the region and to the United States,” Obama told press during a visit to Estonia. “Those who make the mistake of harming Americans will learn that we will not forget, and that our reach is long and that justice will be served.”

Obama said he was “very confident” the US could achieve this objective, adding, “we will not be intimidated.”

The fundamentalist army, which calls itself a caliphate, has conquered territory throughout northern Iraq and has held court in Syria’s eastern provinces for over a year.

Sotloff, 31, an Israeli-American journalist, was killed this week by Islamic State fighters seeking retribution against the US for its air campaign against their assets throughout northern Iraq. Asked whether the US had known of Sotloff’s Israeli citizenship, State Department spokeswoman Jen Psaki said that Washington was “made aware at some point in time” during his captivity.

“The videos were not shot at the same time, with the video of Mr. Sotloff shot after the Foley video,” Psaki told reporters, remarking that the US government learned of the video when it was made public.

A video of his killing shared online was authenticated by the US and UK intelligence communities overnight.

“We will follow them to the gates of hell until they are brought to justice,” Vice President Joe Biden said from New Hampshire, responding to the murders, “because hell is where they will reside.”

Despite his use of hardened words, Obama said that a strike against Islamic State targets in Syria “might require congressional approval,” a request far from guaranteed in a midterm election year.

In September 2013, the White House failed to secure enough votes in Congress to authorize the use of force in Syria after its embattled president, Bashar Assad, gassed more than 1,400 civilians with the chemical weapon sarin.

Members of Congress have remained largely quiet on whether the president would be required to seek authorization for targeted air strikes in Syrian territory.

The Obama administration still considers Assad an illegitimate leader, Psaki said on Wednesday, condemning his army for “de facto carpet bombing” a densely populated neighborhood in Damascus over the last several days with hundreds of rockets.

“The regime is targeting communities that are also confronting ISIL,” Psaki said.

In the video of Sotloff, the killer – a masked Londoner believed to have killed Foley in August – threatens to next kill David Cawthorne Haines, a Briton, should US air strikes continue.

British Prime Minister David Cameron responded angrily to the developments, threatening to join the US air campaign.

Obama seeks a broad coalition of partners that will provide military, humanitarian and financial aid for the fight, led not only by the US, but by Sunni states, in a unique position to claim moral authority over Islamic State, which claims to represent Sunni Islam.

State-run press in Saudi Arabia, the region’s largest Sunni power, published on Wednesday that the kingdom would participate in such a coalition and is seeking partners throughout the region to join the effort.

After a NATO meeting in Wales ends on Friday, Kerry will travel to the Middle East to shore up support for the Saudis and their neighbors.

Religious and government officials in Jordan, Turkey, Qatar and Egypt have condemned the group as un-Islamic.

In her daily briefing, Psaki declined to provide an exhaustive list of countries that the US would attempt to rally to its side. But when specifically asked about possible roles for the governments in Moscow and Tehran, Psaki suggested neither could provide constructive roles.

“They can play a role by encouraging inclusivity,” Psaki said. But “beyond that, no, we’re not working with Iran in this regard.”

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