China supports Iran's membership in the Shanghai Cooperation Organisation (SCO) security bloc, and the subject will be discussed at the group's annual summit which starts on Thursday in the Kazakh capital Astana.
The SCO refused to initiate Iran's accession last year despite a request from Russia which backs Tehran's bid, indicating possible divisions on the issue between Beijing and Moscow, the co-leaders of the SCO.
Iran has long knocked at the SCO's door. Russia argues that with Western sanctions against Tehran lifted, it could finally become a member of the bloc which also includes four ex-Soviet Central Asian republics.
Assistant Chinese Foreign Minister Li Huilai said Iran is an observer at the SCO and has for a long time "proactively participated" in its activities and made positive contributions to the SCO's development.
"China highly appraises this. China welcomes and supports Iran's wish to become a formal member of the SCO," he told reporters, ahead of the Astana summit which President Xi Jinping will attend.
"I think that at this meeting all sides will continue to conscientiously study the issue of Iran becoming a member on the basis of the SCO's relevant rules and consensus through consultations."
China has close economic and diplomatic ties with Tehran. Beijing was also instrumental in pushing through a landmark 2015 deal to curb Iran's nuclear programme.
Li said that Pakistan and India will formally join the bloc as members at the summit, saying that the grouping's attraction to others and its influence continues to grow.
"More and more countries have said they hope to become dialogue partners, observers or formal members of the SCO. China welcomes countries who want to and who meet the conditions to apply to become members, observers or dialogue partners."
China said in November it was willing to consider any application from NATO-member Turkey to join the SCO, after Turkish President Recep Tayyip Erdogan said his country could join.
China, Russia, Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan formed the SCO in 2001 to fight threats posed by extremists in the region and drug trafficking from neighbouring Afghanistan.