Qatar's foreign minister said the country will never surrender to the pressure being applied by its Arab neighbours and will not change its independent foreign policy to resolve disputes that have put the region on edge.
The list, released on Thursday, includes the chairman of the International Union of Muslim Scholars, Yusuf al-Qaradawi.
"This is in light of its commitment to fighting terrorism, drying up the sources of the funding of terrorism, combating extremist ideology and the instruments of spreading and publicising it, joint action to end it and fortify societies from it," the statement read.
"[This is] as a result of the continued violation of the authorities in Doha of the commitments and agreements it signed, including the commitment to not support or shelter elements or groups that threaten the security of countries."
The 18 Qataris named on the list include businessmen, politicians and senior members of the ruling family, including a former interior minister.
Saudi Arabia and allies including the UAE, Bahrain and Egypt - which is not a Gulf Cooperation Council member - on Monday cut diplomatic ties with fellow GCC state Qatar over claims that it supports "extremism".
Qatar strongly denies the allegations.
"We are not prepared to surrender, and will never be prepared to surrender, the independence of our foreign policy," Sheikh Mohammed bin Abdulrahman Al Thani told Al Jazeera.
He also said Qatar's Emir Sheikh Tamim bin Hamad Al Thani would not leave the country while it was "in blockade", and therefore could not attend an offered mediation by US President Donald Trump at the White House.
Source: Al Jazeera and news agencies