In his strongest statement of support for Qatar in the nearly three-week-old crisis centered on the Gulf state, Erdogan said the call to withdraw Turkish forces was disrespectful and that Doha - which described the demands as unreasonable - was taking the right approach.

Saudi Arabia, the United Arab Emirates, Egypt and Bahrain imposed a boycott on June 5 on Qatar and issued 13 demands including closing Al Jazeera television, curbing relations with Iran, shutting the Turkish base and paying reparations.

Doha said it was reviewing the list, but said it was not reasonable or actionable.

"We approve and appreciate the attitude of Qatar against the list of 13 demands," Erdogan, speaking outside a mosque in Istanbul, said. "...This approach of 13 demands is against international law because you cannot attack or intervene in the sovereignty of a country."

The demands are apparently aimed at dismantling Qatar's interventionist foreign policy .

Both Qatar and Turkey, whose ruling AK Party has its roots in Islamist politics, backed a Muslim Brotherhood government in Egypt before it was overthrown in 2013. The Arab states have demanded Qatar cut any links to the Brotherhood and other groups they deem to be terrorist, ideological or sectarian.

Bahrain's state news agency on Sunday confirmed the demands set out by un-named Gulf officials on Friday, including that Qatar close the Turkish base, end military cooperation with Ankara inside Qatar and stop supporting militant groups.

"The demands aim to achieve regional countries' stability, stand firmly against foreign interference and stop support for terrorist organizations," it said.