President Recep Tayyip Erdogan on Sunday dismissed calls for the closure of a Turkish military base in Qatar.
It is on a list of demands made by four Arab states in return for lifting sanctions on the Gulf emirate which they accuse of supporting terrorism.
Qatar denies this, calling the ultimatum unreasonable. Its stance is backed by the Turkish leader.
“This approach of 13 demands is against international law because you can’t attack or intervene in the sovereignty of a country,” Erdogan said in Istanbul, in his strongest statement of support yet for Qatar in this three- week-old crisis.
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.
Erdogan said calls to withdraw his country’s troops from Qatar were disrespect to Turkey.
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.
Erdogan said Turkey had also offered to establish a military base in Saudi Arabia, but never received a clear answer.
Ankara has sent supplies to Qatar since its neighbours cut air and sea links. It has also rushed through legislation to send more troops to its base in Doha.
Speaking outside the Istanbul mosque after prayers marking the Muslim Eid al-Fitr holiday, Erdogan said he would continue his planned programme despite feeling briefly unwell.
“I had a little condition about my blood pressure, related to my diabetes,” he said.