US President Barak Obama received the support in a meeting Tuesday with senior representatives of the five Arab countries and Iraqi Prime Minister Haider Al Abadi during their participation in the UN General Assembly sessions.
Obama came out of the meeting saying that everyone stood "united" on the matter, a US diplomatic source said.
"There was a unanimous decision. All those who were in this meeting are involved in this long-term," the source told journalists on the condition of anonymity.
"The president received a message 'We are with you and we are with you until the end'," he said.
The meeting was attended by King Abdullah of Jordan, Saudi foreign minister Prince Saud Al Faisal, Sheikh Khalid Bin Ahmed Bin Mohammed Al Khalifa of Bahrain, Khalid bin Mohammad Al Attiyah of Qatar and Sheikh Abdullah bin Zayed Al Nahyan of the UAE.
All five countries took part in US-led air strikes on the IS in Syria earlier in the week.
Before the meeting, Obama told the press that the fight against jihadi groups would neither be "quick" nor "easy", but would show the international community's "clear message" against Islamic radicalism.
"Thanks to the efforts of this unprecedented coalition, I believe that we now have the opportunity to send a clear message that the world is united," he added.
US Secretary of State John Kerry said Tuesday that over 50 countries, including Turkey, have already joined the US-led international coalition against the IS.
Mexico, Tunisia, Switzerland, Singapore, Georgia and Taiwan were among the latest countries to pledge their support in some form or the other to the coalition, according to the US State Department.The US prefers that each country decides on its commitments to the alliance, which, apart from military strikes, will also impose economic measures against the IS and make efforts to prevent more foreign fighters from being recruited by the terrorist group.