DUBAI (Reuters) - Kuwait has advised citizens to make sure their phones contain no material that might be seen as being linked to Islamist militants before traveling to the United States, local media reported on Saturday, after three men were denied entry in July.

State news agency KUNA quoted a statement by the Kuwaiti embassy in Washington as saying that authorities at "some U.S. airports may check the contents of mobile phones or other smart mobile equipment".

"The embassy of the state of Kuwait in Washington urged citizens to make sure that their phones do not contain any materials or photos of extremist nature, related to areas of conflict or terrorist organizations or footage of violence of all kinds before entering U.S. territories," KUNA said, citing a statement.

"(This is) so that students and citizens may be spared questioning by authorities in U.S. airports and to avoid any action against them that could result in cancelling their visas and banning them from entering U.S. territories," it added.

The Arabic language al-Rai newspaper reported in July that three businessmen were questioned for 21 hours at Los Angeles airport and had their telephones checked before they were turned back, in the second incident of its kind this year.

The Gulf Arab OPEC oil exporter is a key U.S. ally and a member of an international alliance led by the United States which is fighting against Islamic State in Syria.

In July, the United Arab Emirates, another close Gulf Arab ally of the United States, told its male citizens to avoid wearing traditional white robes and head dress when traveling abroad, after a businessman was wrestled to the ground at an Avon, Ohio hotel and held as an Islamic State suspect.

(Reporting by Sami Aboudi)