"I want to clearly say that we disapprove of the sanctions on Qatar," Recep Tayyip Erdogan said.
"These developments, coming at a time when we need solidarity and cooperation more than ever, are no good for any country in the region."
Erdogan's remarks came as he addressed a fast-breaking iftar dinner organized by his ruling Justice and Development (AK) Party in the capital Ankara.
Tuesday the president also continued his diplomatic efforts to defuse tensions between Qatar and the countries which have accused it of supporting terrorism.
Earlier on Monday, Saudi Arabia, Egypt, the United Arab Emirates, Bahrain and Yemen cut links with Qatar, in the worst rift in years among major states in the Arab world.
Qatar says the "baseless" allegations that it supports terrorism are being used to tarnish the image and unity of Gulf states.
According to presidential sources, Erdogan had phone calls with French President Emmanuel Macron, Indonesian President Joko Widodo, Malaysian Prime Minister Najib bin Tun Abdul Razak, Bahrain's King Hamad bin Isa Al-Khalifa, Jordan's King Abdullah II, and Lebanese Prime Minister Saad Hariri.
These followed Monday phone calls with Qatari Emir Sheikh Tamim bin Hamad al-Thani, Russian President Vladimir Putin, Kuwaiti Emir Sheikh Sabah al-Ahmad al-Jaber al-Sabah, and King Salman bin Abdulaziz Al Saud of Saudi Arabia.
Erdogan told the leaders that regional problems should be solved through dialogue, said the sources, who spoke on condition of anonymity due to restrictions on speaking to the media.
If needed, Turkey stands ready to do whatever it can, Erdogan said.