(ANKARA) - Four EU nations and Turkey signed Wednesday supplementary deals for the construction of a long-delayed gas pipeline, designed to reduce reliance on Russia, amid lingering uncertainty over suppliers.

Meeting in the central Turkish town of Kayseri, government and company officials from Austria, Bulgaria, Hungary, Romania and Turkey inked the "project support agreements" for the Nabucco pipeline, Anatolia news agency reported.

The deals finalise the legal framework, aiming to ensure to ease the pipeline scheme through EU and Turkish legislation and protect it from potential discriminatory changes in the law, according to a statement by the Nabucco consortium.

The inter-governmental accord for the conduit was signed in Ankara in July 2009.

An ambitious and costly project, the pipeline aims to bring gas from central Asia to Europe, bypassing Russia and Ukraine, where repeated squabbles over prices have in the past left members of the 27-nation European Union without vital supplies of gas, sometimes in mid-winter.

However, the companies building the pipeline -- OMV of Austria, MOL of Hungary, Romania's Transgaz, Bulgaria's Bulgargaz, BOTAS of Turkey and RWE of Germany -- have yet to sign a single contract with any of a number of potential supplier countries.

The 3,900-kilometre-long pipeline was originally expected to become operational in 2014, but start of construction has been rescheduled to 2013, with the first gas expected to flow in 2017.

To be built at an estimated cost of 7.9 billion euros ($11.5 billion), the pipeline will have a capacity to pump 31 billion cubic metres of gas to Austria via Turkey and the Balkans.

Azerbaijan is seen as the primary potential provider of gas, with Turkmenistan, Iraq and Egypt also mentioned for the long term.

Nabucco is in competition with Russia's South Stream project, which will carry Russian gas through Bulgaria to Western Europe under the Black Sea.