Kuwait briefly detained a prominent Sunni Muslim cleric less than two weeks after the US included him on a sanctions list on suspicion he was funnelling money to militants in Iraq and Syria, his lawyer said on Monday.

Shafi Al-Ajmi, who was detained on Sunday on the border with Saudi Arabia while returning home from a pilgrimage, was released after four hours of questioning, his lawyer said.

"He was released without any charges," the lawyer, Mohammed Al-Jumia, told Reuters. "He is now at home."

Jumia said he planned to file a lawsuit against the US Treasury to lift his client's name from its blacklist, but gave no further details.

An Interior Ministry spokesman could not immediately be reached for comment.

Kuwait has been one of the biggest humanitarian donors to Syrian refugees through the United Nations, but it has also struggled to control unofficial fundraising for opposition groups in Syria by private individuals.

The government has stepped up its monitoring of individuals and charities suspected of collecting donations for militants linked to Al Qaeda in Syria and in Iraq.

On August 6, the US imposed sanctions on Shafi and two other men suspected of funnelling money from Kuwait to Islamic State, the Al Qaeda splinter group that has seized swathes of territory in Iraq and Syria. Washington also said the men had helped smuggle fighters to Afghanistan and Iraq. - Reuters