(Associated Press) – Uzbekistan says it will cease natural gas deliveries to its energy-starved neighbour Tajikistan starting next month.

Uzbekistan, which is Tajikistan’s only external source of gas, routinely suspends deliveries amid complaints of non-payment. Uzbekneftegaz said in a statement Sunday the suspension was in line with a three-month contract signed at the start of the year.

Energy officials in Tajikistan had complained about plans to halt deliveries.

Relations between the two former Soviet Central Asian states have been strained ever since they both gained independence in 1991. Tajikistan largely relies on its neighbours, and especially Uzbekistan’s railroads and highways, for overland transportation infrastructure. The railway stretch impacted by the explosion happens to be vital for transporting fuel, food and other supplies to Khatlon oblast in Southern Tajikistan, whose remoteness makes resupply via Tajikistan’s infrastructure costly and impractical during winter.

In mid-November, Uzbekistan unilaterally closed a railway line between the Uzbek town of Termez and the Tajik city of Qurghonteppa in Khatlon oblast, not far from Uzbekistan’s border with Tajikistan and Afghanistan. After a few days of silence, Uzbek authorities explained the shutdown of rail traffic as the result of an explosion, a mysterious terrorist attack that damaged the connecting railway bridge.

The railroad remains closed, which has resulted in as many as 300 freight cars being stuck in Uzbekistan. These hold all sorts of goods and essentials, including humanitarian aid. This has caused substantial shortages and financial losses in Tajikistan and induced scarcity and price hikes in Khatlon oblast. The head of the World Food Program, Alzira Ferreira has accused the Uzbek authorities of deliberately refusing to allow freight and warned that such substantial delays may have severe consequences for the local population.

Uzbekistan is also angered by Tajikistan’s long-term plans to build a hydropower plant it says will cut off major irrigation routes.