Israel has been aiding the US military campaign against Islamic State militants in Iraq by providing Washington with intelligence information – including satellite images detailing extremists' positions and movements.

A diplomatic source told Reuters that Israeli spy satellites flying over Iraqi territory captured photos of militant positions in the country at frequencies and angles that were not available to US satellites. Sharing those images with the US Department of Defense allowed US forces to “fill out its information and get better battle damage assessments” following strikes on Islamic State (IS) positions, the source said.

It is also alleged that Tel Aviv offered Washington information from an international travel database leaking the names of suspected Western jihadists allegedly fighting for the Islamic State.

“The Israelis are very good with passenger data and with analysing social media in Arabic to get a better idea of who these people are,” the diplomat said on condition of anonymity, adding that the provided data was shared with Arab and Turkish allies after “Hebrew and other markings [were] scrubbed out.”

“There is significant concern about the idea that some of these individuals may try to travel back to the West, using the Western passports, and carry out acts of violence or engage in terrorism here,” White House press secretary Josh Earnest said Monday.

The Israeli Defense Ministry did not confirm or deny the involvement of the international military effort against IS.

“We don't comment on any assistance by us, or if there is such assistance, in the fight against ISIS,” said ministry spokesman Yaacov Havakook.

The revelation comes as the US tries to unite a coalition of the willing. US Secretary of State John Kerry is scheduled to visit the Middle East this week.

Kerry will have bilateral discussions with Jordanian and Saudi officials, as well as consultations with “key partners and allies” in the region, spokeswoman Jennifer Psaki said in a statement, adding that more than 40 countries have formed a coalition against IS.

“There are obviously a range of capabilities or capacities that different countries have,” Psaki told reporters. “The focus will be on multiple lines of effort, including military support to our Iraqi partners, stopping the flow of foreign fighters, countering ISIL's financing and funding, addressing humanitarian crises, and de-legitimizing ISIL's ideology.”

Meanwhile, Earnest said that Barack Obama is trying to build a broader international coalition by “engaging regional governments [and] looking for the support and the effective governance of the Iraqi central government to confront this threat.”

The US has already carried out more than 120 airstrikes against the Islamic State in Iraq, with warplanes bombing IS targets since August 8.