He made the remarks in a phone conversation with Iranian President Ebrahim Raisi.
Xi pointed out that since the establishment of China-Iran diplomatic ties 50 years ago, bilateral relations have stood the test of international changes, with the friendship between the people of the two countries growing ever stronger.
In the face of a complicated situation that combines profound global changes and a pandemic both unseen in a century, China and Iran have stood together and helped each other, Xi noted.
While working together against COVID-19, the two countries have strengthened solidarity and coordination, made positive progress in practical cooperation, effectively cemented strategic mutual trust, and firmly defended international fairness and justice, he said.
China appreciates Iran's active efforts to develop bilateral relations, Xi said, stressing that no matter how the international and regional situation changes, China will unswervingly develop friendly relations with Iran.
The two sides, he suggested, should continue to support each other on issues related to their core interests and major concerns.
China firmly supports Iran in safeguarding its sovereignty and national dignity, and opposes external interference, he said, adding that China is willing to work with Iran to enhance experience sharing on state governance, strengthen cooperation in pandemic response, advance their respective development, and promote the people's well-being in both countries.
The plan for China-Iran comprehensive cooperation has opened up broader prospects for deepening bilateral win-win cooperation, Xi said, adding that the two sides should tap deeply into their potential, actively promote Belt and Road cooperation, and produce more results in practical cooperation.
China, Xi said, supports Iran's legitimate concerns on the comprehensive agreement on the Iranian nuclear issue, and stands ready to strengthen coordination and cooperation with Iran on regional affairs, so as to jointly safeguard common interests and promote regional security and stability.
For his part, Raisi expressed warm congratulations on the 100th anniversary of the founding of the Communist Party of China and the 50th anniversary of the establishment of diplomatic ties between Iran and China.
It is a foreign policy priority and focus of the Iranian government to steadfastly develop a more robust comprehensive strategic partnership with China, he said.
The Iranian side, he said, thanks China for providing Iran with valuable support to fight against the COVID-19 pandemic, appreciates China's fair positions on international and regional affairs, including the Iranian nuclear issue.
Iran stands ready to work with China to intensify strategic communication, enhance strategic mutual trust, deepen bilateral cooperation and multilateral coordination, and jointly oppose unilateralism, hegemonism and external interference, Raisi added.
The Iranian side firmly supports China's positions on issues concerning Taiwan, Xinjiang and Hong Kong, and staunchly opposes certain countries using the issue of COVID-19 origins tracing as a pretext to suppress and contain China, he said.
China's Belt and Road Initiative brims with strategic vision, and Iran is willing to actively participate in it, he added.