Turkish President Erdogan says the conditions put forward by Saudi Arabia and three other states for lifting sanctions on Qatar were "against international law".
Turkish President Recep Tayyip Ergodan said on Sunday that he backed Qatar's response to a list of demands issued by Arab states boycotting the Gulf emirate, and said calls to shut down a Turkish military base there were disrespectful.
Qatar has described the pressure by its larger neighbours as an "illegal blockade" aimed at curbing its sovereignty, and said that the ultimatum by Saudi Arabia, the United Arab Emirates, Egypt and Bahrain was "unreasonable".
The sanctions have disrupted Qatar's main import routes by land from Saudi Arabia and by sea from big container ships docked in the UAE. But Qatar so far has avoided economic collapse by quickly finding alternative channels and says its huge financial reserves will meet any challenges.
Erdogan said Turkey appreciated and endorsed Qatar's response to the 13 demands, which include closing the Al Jazeera satellite television network, curbing relations with Iran and shutting a Turkish base in Qatar.
"We consider these demands are against international law," Erdogan told reporters after Eid al-Fitr prayers in Istanbul.
"It is a breach of Qatar's sovereign rights."
Erdogan said Turkey had offered to set up a military base in Saudi Arabia as well as Qatar, but Riyadh had not responded.
"Even though they still didn't come back to us on this, asking Turkey to pull back its troops (from Qatar) is disrespectful against Turkey," he said.
Saudi Arabia, UAE, Bahrain and Egypt have given Qatar a 10-day deadline to meet the demands.