Corker's opposition includes all six members of the Gulf Cooperation Council - the five countries involved in the Qatar dispute, as well as Kuwait, which has been acting as a mediator.
"We consider these demands are against worldwide law", Erdogan told reporters after Eid al-Fitr prayers in Istanbul. Ankara also moved to meet the shortfall in food supplies to Qatar, much of which previously came across the Saudi border.
The Arab states are demanding, among other things, that Doha close Al Jazeera television, curb ties with Iran, shut a Turkish base and also pay reparations.
"The unity of the Gulf States and their commitment to security cooperation were welcome steps forward", Corker wrote in the letter to Tillerson.
Diplomatic relations were cut with Qatar by four Arab neighbors including Saudi Arabia, the United Arab Emirates, Bahrain and Egypt on June 5 who accused the small oil-rich country of having ties with "terrorist organizations", including the Muslim Brotherhood. "The kingdom can not allow Turkey to set up a military base on its territory", said a statement carried by SPA state news agency.
"You'd expect there to be a very big red line drawn by the USA on that, especially given that Qatar is home to its most important military base in the Middle East", he said.More news: North Korea: Warmbier's death a 'mystery to us'
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"It is a breach of Qatar's sovereign rights".
Interference: Stop interfering other countries' domestic affairs. At the same time, the director of Qatar's government's communications office, Sheikh Saif Al Thani, called the Gulf States' demands "unrealistic" and said they were aimed at limiting Qatar's sovereignty. "I made this offer to the king himself and they said they will consider this".
"You'd expect there to be a very big red line drawn by the US on that, especially given that Qatar is home to its most important military base in the Middle East".
In a sign of support, the Turkish parliament swiftly ratified a 2014 military agreement with Qatar earlier this month, allowing the deployment of troops to its base there.
Qatar, which had 10 days to respond, is still gauging how to answer. Turkey's former ambassador to Qatar in late 2015 told Reuters that 3,000 ground troops could eventually be deployed.
Some demands set by four Arab states on Qatar in return for lifting sanctions will be "difficult to meet", US Secretary of State Rex Tillerson says.
The top U.S. diplomat also said Washington was backing mediation efforts by Kuwait aimed at defusing the crisis and urged the different sides to "sit together" and continue discussing. Tillerson also reiterated that the common goal of the USA, the Gulf States and Qatar is "stopping terrorism and countering extremism" and added that "each country involved has something to contribute to that effort".