UPDATE 4-Nabucco gas intergovernment deal to be signed July 13

* Nabucco transit accord to be signed July 13

* Romania says Turkish throughput issue solved

* Agreement to boost competition with rival Russian pipeline

(Adds comment from Russian Energy Minister)

By Zerin Elci and Radu Marinas

ANKARA/BUCHAREST, July 3 (Reuters) - An intergovernmental transit agreement for the Nabucco natural gas pipeline will be signed in Ankara on July 13, the European Union said on Friday, confirming statements from Romania and Turkish sources.

The pipeline, intended to relieve European dependence on Russian gas, is expected to bring Caspian and Middle East gas to Europe as early as 2014, but the project has been delayed by lack of supplies and infighting among stakeholders.

A firm transit agreement could increase competition between Nabucco and a rival Russian pipeline, allowing the EU-backed project to start work on open-season agreements, when firms buy up portions of the pipeline's 31 billion cubic metre capacity.

"On July 13, the intergovernmental accord on Nabucco will be signed in Turkey," Romanian Economy Minister Adriean Videanu told Reuters by telephone from Azerbaijan where he is on a two-day visit.

The European Union confirmed it had received an invitation to the July 13 signing ceremony.

"I can confirm that the Commission has received an invitation to the signing ceremony of the intergovernmental agreement on the Nabucco pipeline on July 13 in Ankara," a European Commission spokesman told a news briefing.

Jose Manuel Barroso, President of the European Commission said the Nabucco project was crucial for Europe's energy security.

"15 PERCENT ISSUE"

The signing of the transit agreement was delayed by demands from Turkey, which has few hydrocarbon resources of its own, that it uses 15 percent of Nabucco's 31 billion cubic metre capacity throughput for its domestic usage or for re-export.