WASHINGTON (AP) — The Islamic State group doesn’t pose an immediate threat of an attack in the United States, senior U.S. officials testified Wednesday, but warned that the danger from the militants is spreading beyond the Middle East to Europe and other parts of the world.

They have the ability to attack American targets overseas with little or no warning, the officials said.

Francis Taylor, the Homeland Security Department’s undersecretary for intelligence and analysis, said the Sunni extremist fighters in Iraq and Syria have capabilities most terrorist organizations don’t possess. But he said his department is currently unaware of any credible threat to the U.S. homeland from the Islamic State.

Testifying alongside Taylor before the Senate Homeland Security and Governmental Affairs Committee, Nicholas Rasmussen, deputy director of the National Counterterrorism Center, said attacks in France and Belgium by Europeans who’ve fought with the group show its expanding ambitions and reach.

“The United States is not immune,” Rasmussen warned. If the militants are left unchecked, he said, the threat will grow to all states the group considers “apostate” — or those which reject what it believes to be the true faith. The U.S. would be one of these, he said.

The hearing took place hours before President Barack Obama was to address the nation on an expanded military and political effort to combat Islamic State militants in Syria and Iraq. The president was expected to urge Congress to quickly give him authority to arm Syrian opposition forces fighting President Bashar Assad and raise the possibility of expanding U.S. airstrikes, currently limited to Iraq, to include Islamic State bases and supply networks in Syria.

The Senate’s top Democrat backed the idea of giving Obama greater authority to aid moderate Syrian rebels to fight both Assad’s government and the Islamic State militants who’ve in recent months overrun large parts of Iraq and beheaded two American journalists. Sen. Harry Reid, D-Nev., however, lashed out at the idea of rushing into a war like the one in Iraq last decade, harshly criticizing former Vice President Dick Cheney a day after Cheney spoke to House Republicans.

A House GOP spending bill unveiled Tuesday night doesn’t include authority for Obama to train and equip Syrian forces, and it’s unclear whether it will be added in before lawmakers vote on it Thursday.

Republicans have been demanding that Obama present a detailed plan to defeat the militants.

Pressed at the hearing by Sen. Ron Johnson, R-Wis., Rasmussen said he saw a multi-phased strategy emerging. The immediate goal would be to degrade the Islamic State group’s ability to launch attacks, he said, while the long-term effort to destroy the group would take longer.

Taylor outlined several steps U.S. officials have taken to increase security.

Aviation security changes since July have made it harder for terrorists to try to get explosives onto civil aircraft, he said. Increased intelligence-sharing with other governments has helped identify Westerners and other foreigners fighting with Islamic State extremists in Syria.

More than 100 Americans have traveled to Syria to fight for various militant groups or tried to make the journey or intend to, officials said. Previously, U.S. officials said more concretely that up to 100 U.S. citizens were fighting in the country.