Turkmenistan on August 12 cautioned Russia that it should not try to extend its influence over the Central Asia-China natural gas supply chain.

Its comments came after Moscow said more countries could join its emerging "gas union" with Kazakhstan and Uzbekistan.

Turkmenistan's foreign ministry was reported by Reuters as responding that although Russia's comments were vague, Ashgabat wanted to make it clear that it has not been consulted on the possible addition of new suppliers to the pipeline that is used to send Central Asian, and largely Turkmen, gas to China.

"The Turkmen side considers such an approach incomprehensible and unacceptable, and out country views it as going against international law and the established practice in the gas sector," the foreign ministry was reported as saying in a statement.

Turkmenistan, Uzbekistan and Kazakhstan all pump gas to China via a pipeline that crosses the three countries.

Russia has been trying to open up new Asian markets for its gas since Western sanctions hit Moscow following its invastion of Ukraine. It said last year that it was putting together a gas union with Kazakhstan and Uzbekistan. Advantages, it said, would be a streamlining of the shipping and exporting of gas to the two countries plus to third parties.

So far, the only clear practical move the union has made is the introduction of a plan to reverse a gas pipeline that connects Turkmenistan, Uzbekistan and Kazakhstan to Russia. The reversal will enable Russia's Gazprom to transit gas to Uzbekistan, which has started experiencing energy shortages.

Though Russia's foreign ministry has said that the gas union could be expanded, it has not named any countries that are interested in joining it.