Iran is keen to build closer military ties with China, welcoming Beijing to expand its naval presence and urging it to play a bigger role in the Tehran nuclear talks, the South China Morning Post said in an article published on Monday.

The two states might conduct more port calls because of China’s growing commercial interests, Ali Akbar Velayati, a senior aide to the Supreme Leader of the Islamic Revolution told the South China Morning Post.

Last month, Russia hosted Chinese navy vessels in the Black Sea ahead of the two countries’ joint exercises in the Mediterranean Sea. The move raised concerns about China’s growing maritime force.

But Velayati said, “It is right for China, as a great power, to do that. You see the United States is also sending its military vessels everywhere. It is China’s right to send its military vessels.”

The Chinese and Iranian militaries conducted a series of exchanges in 2013 and 2014.

Last year, Chinese Defense Minister Chang Wanquan told Iranian Navy Commander, Rear Admiral Habibollah Sayyari, that the two forces had seen “good cooperation” on mutual visits.

In 2013, an Iranian destroyer and helicopter carrier docked at the port city of Zhangjiagang in Jiangsu province after a 40-day voyage. In 2014, two Chinese destroyers paid a four-day visit to Iran’s Persian Gulf port of Bandar Abbas.

Velayati described the port calls between China and Iran as “friendly behavior between the two countries”.

“It is quite natural,” he said. “We have to support the transshipment of goods between Iran and other countries. The same right applies to China. It is the right of a country to defend its own transshipment of goods.”

The Iranian adviser’s remarks come ahead of a June 30 deadline to strike a deal on Iran’s nuclear program with the 5+1 group of world powers, comprising China, Russia, the United States, Britain, France, and Germany.

Tehran reached a framework agreement with the group in April, but diplomats remain skeptical about whether a final deal can be reached by the end of the month.

Chinese Foreign Minister Wang Yi told his Iranian counterpart Mohammad Javad Zarif last week that Beijing called on all parties involved in the talks to show political wisdom for the sake of progress, and China was willing to step up coordination with Tehran.

Velayati declined to say if he was optimistic about reaching an agreement.

He called on China and Russia to better coordinate with Iran to push forward the talks, saying this could be achieved by having more discussions between the three states before negotiations with the larger 5+1 group.

“China and Russia have had a moderate position in the negotiation,” the adviser said. “If the Chinese position is more active, it will affect the continuation of the positive result of the talks.”

On the economic front, Velayati said energy trade between China and Iran had improved and that there was “no limit” on Iran’s capacity to export oil to China.

“There is no ceiling for the volume of oil and gas we are going to send to China,” he said. “It depends on the demands of the Chinese companies.”

China imported 2.91 million tons of crude oil a day from Iran in April, up 10.8 percent from March. It also imported $2.1 billion of non-oil goods from Iran in the first quarter of the year. Asadollah Asgar Oladi, the head of Iran-China Chamber of Commerce, recently said Beijing have agreed that China would pay in cash for the oil and gas it purchased from Tehran.