US President Barack Obama says he will not hesitate to take action against Islamic State (IS) militants in Syria as well as Iraq.
In a nationally televised speech outlining his strategy against IS, he said that any group that threatened America would “find no safe haven”.
He also announced that 475 US military personnel would be sent to Iraq but said they would not have a combat role.
IS controls large parts of Syria and Iraq after a rapid military advance.
Its fighters have become notorious for their brutality, beheading enemy soldiers and Western journalists on video.
The US has launched over 150 airstrikes against the group in Iraq and provided arms to Iraqi and Kurdish forces fighting against IS.
In a 15-minute speech shown at peak time in the US, President Obama vowed that America would lead “a broad coalition to roll back” IS.
“Working with the Iraqi government, we will expand our efforts beyond protecting our own people and humanitarian missions, so that we’re hitting Isil [Islamic State in Iraq and the Levant – the previous name for IS] targets as Iraqi forces go on the offense” he said.
He said he would welcome congressional approval for the fight against IS but said that he had the authority to act without it.
President Obama was elected in part because of fervent opposition to the 2003 invasion of Iraq, and presided over the US troop pullout from the country.
Last year President Obama abandoned plans to launch airstrikes in Syria against government forces after congressional opposition.
In his speech, he ruled out working with President Bashar al-Assad of Syria, despite the fact that his forces are also engaged in fighting IS.
“In the fight against Isil, we cannot rely on an Assad regime that terrorises its people: a regime that will never regain the legitimacy it has lost” he said.
Instead, he said, the US would seek to strengthen the non-IS Syrian opposition, which fights against both IS and President Assad.
Syria’s Western-backed National Coalition welcomed Mr Obama’s plan, and urged Congress to approve it.
“The Syrian Coalition… stands ready and willing to partner with the international community not only to defeat [IS] but also rid the Syrian people of the tyranny of the Assad regime,” its president Hadi al-Bahra said in a statement, quoted by Reuters news agency.
US Secretary of State John Kerry is already in the Middle East trying to build a coalition against IS.
Mr Kerry was in Iraq on Wednesday, where he praised the new government’s plans to involve more Sunnis in government and heal ties with the Kurds.