TEHRAN (Reu - Iran said on Tuesday three Americans detained in the country on Friday were being questioned by Iranian authorities, al-Alam television reported.

They are definitely Americans. They were detained four days ago. We don't know whether they are tourists or not. We are questioning them, a local security official in Iran's western Kurdistan province, Iraj Hassanzadeh, told al-Alam.

A source told Iran's Arabic-language station on Saturday that the three, believed to be two men and a woman, had been arrested after entering Iran.

The U.S. State Department has said it was investigating reports that Iran had arrested the tourists.

A senior Kurdish security official, Qadr Hamajan, has said the three who disappeared close to northern Iraq's border with Iran had entered Iranian territory and been arrested.

They arrived in the Kurdish city of Sulaimaniya, 260 km (160 miles) northeast of Baghdad, from Arbil, the capital of Iraq's largely autonomous Kurdish region, on Wednesday.

On Thursday, three out of four of the group went on to the Ahmed Awa tourist resort, east of Sulaimaniya near the Iranian border. The fourth member of the group remained in Sulaimaniya.

A Kurdish official said the group at the resort had unwittingly crossed into Iranian territory while hiking.

There is no clear border marker between Iran and Iraq at Ahmed Awa.

In 2007 Iranian Revolutionary Guards forces seized 15 British sailors in the Shatt al-Arab waterway that separates Iran and Iraq. Iran said the British servicemen had entered its waters illegally.

Iran's President Mahmoud Ahmadinejad later ordered the release of the 15 British sailors as a gift.

Adding to tensions with the West, Tehran has accused Western powers, particularly the United States and Britain, of fuelling unrests in the Islamic state after the country's disputed June presidential election. Washington and London deny the charge.

Moderates say the vote was rigged in favor of Ahmadinejad's re-election but Supreme Leader Ayatollah Ali Khamenei officially endorsed Ahmadinejad's second-term presidency on Monday.

(Reporting by Parisa Hafezi, writing by Zahra Hosseinian, Editing by Samia Nakhoul)