Xi is the second leader of a U.N. Security Council member to visit Tehran after the nuclear deal Iran struck with world powers last year. Russian President Vladimir Putin visited Tehran in November.
Iran emerged from years of economic isolation this month when the United Nations’ nuclear watchdog ruled it had curbed its nuclear program, clearing the way for the lifting of U.N., U.S., and European Union sanctions.
“Iran and China have agreed to increase trade to $600 billion in the next 10 years,” Rouhani said at a news conference with Xi broadcast live on state television.
“Iran and China have agreed on forming strategic relations (as) reflected in a 25-year comprehensive document,” he said.
Iran and China signed 17 accords on Saturday, including on cooperation in nuclear energy and a revival of the ancient Silk Road trade route, known in China as One Belt, One Road.
“China is still heavily dependent on Iran for its energy imports and Russia needs Iran in terms of its new security architecture vision for the Middle East,” said Ellie Geranmayeh, policy fellow at the European Council on Foreign Relations.
“Iran plays quite an integral role for both China and Russia’s interests within the region, much more than it does for the Europeans,” Geranmayeh said.
Xi was quoted as saying by China’s Xinhua news agency: “The China-Iran friendship … has stood the test of the vicissitudes of the international landscape.”
The Chinese state-backed Global Times newspaper said in an editorial on Saturday that China hoped to improve ties with Iran as part of its sweeping plan to rebuild trade links with Europe and Asia and carve out new markets for its goods.
“China is of course considering its self interest in strengthening cooperation with Iran, especially at a time when China is in the midst of expending efforts to push forward the One Belt, One Road initiative, Iran is an important fulcrum,” the paper said.
Rouhani said the countries had also agreed to cooperate on “terrorism and extremism in Iraq, Syria, Afghanistan and Yemen”.
China signaled its support for Yemen’s government, which is fighting an Iran-allied militia, during Xi’s visit to Saudi Arabia, Iran’s rival for influence in the region, this week.
Iran has called on China to join the fight against the Islamic State militant group and play a more active role in the region.
Tehran is widely credited with convincing Russia to start its military intervention in Syria and join the fight against Islamic State.
“Although China and Russia backed U.N. sanctions against Iran on its nuclear program, they were also heavily pushing for special waivers to continue trading with Iran,” Geranmayeh said.
“Iran had a relationship both politically and economically with China and Russia for the last ten years in ways that it hasn’t had with Europe. So it’s quite natural to see it opening up first to these countries.”
The Chinese president was to meet Iran’s most powerful figure, Supreme Leader Ayatollah Ali Khamenei, later in the day.