The two neighbours lie in Central Asia, a region that the UN says is more affected by climate change than the global average, and where water shortages are a regular source of tension between countries.

The Syr Darya flows through four Central Asian countries (Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan) and is under threat from agricultural overuse, wasteful use of water and climate change.

"Kazakhstan and Uzbekistan have agreed on the specific techniques to track the metering of water on the Syr Darya river," Kazakhstan's ministry of hydro resources and irrigation said.

The announcement comes months after the countries, both mostly covered by steppe and desert, identified the 10 zones where the water meters would be located.

According to Kazakhstan, the agreement should "ensure total transparency in water measurements".

Kazakhstan said it is "actively promoting this issue in negotiations with Kyrgyzstan and Tajikistan" -- which have had disputes over control of water resources.

Despite growing and unprecedented inter-state cooperation in recent years, the water-sharing system in Central Asia -- inherited from the Soviet era -- remains fragile in this region of some 80 million inhabitants.

Countries currently exchange water -- necessary not only for agriculture use but also to power hydroelectric plants -- according to a precise schedule.

At over 2,200 kilometres (1,370 miles) long, the Syr Darya is estimated to be the longest river in Central Asia, ahead of the Amu Darya.

Both rivers of this landlocked region were over-exploited in the Soviet era, notably for cotton crops, which contributed to dry up the Aral Sea.

This trend was made worse by climate change -- particularly acute in Central Asia, where it is melting glaciers that feed the rivers -- and by the wasteful use of water, due to ageing infrastructure.