By Oana Lungescu
BBC News, Prague
Work is scheduled to start on Nabucco in 2011, with the first deliveries in 2014
The EU has signed an energy agreement with several countries aimed at developing a "southern corridor" for gas supplies bypassing Russia.
The agreement was signed by the leaders of Azerbaijan, Georgia, Turkey and Egypt at a summit in Prague.
It commits them to speeding up the construction of a long-delayed pipeline to bring Caspian gas to Central Europe.
The EU is anxious to improve energy security because a Russia-Ukraine row in January cut gas supplies.
Key to this meeting was a commitment by Turkey's President Abdullah Gul to sign up to an agreement on the construction of the Nabucco gas pipeline by next month.
In a symbolic gesture, the agreement is to be signed in Turkey, after years of haggling over transit rules.
But Mr Gul also made clear he expected some progress on Turkey's stalled EU membership talks.
It is hoped the Nabucco pipeline, which will stretch for 3,300km (2,050 miles) between Azerbaijan and Austria, will start pumping gas by 2014.
But Russia, which supplies one-fifth of Europe's gas, is nervous about any pipeline it does not control and its deputy energy minister repeated long-standing concerns about Nabucco.
The representatives of Kazakhstan, Turkmenistan and Uzbekistan refused to sign the agreement in Prague, because - diplomats said - of Russian pressure.
Iraq, which was also invited at the meeting, did not send anyone, although it is expected to sign an agreement on energy with the EU soon.
The EU's new "southern corridor" has been dubbed the "modern Silk Road".
A Czech official involved in the talks said the EU had no time to lose.
For 15 years, he said, the EU had just been talking and not being serious - now it has to put its money where its mouth is.
Otherwise, he warned, Central Asian countries would be pushed to sell their gas to Russia and energy prices in Europe would skyrocket.
Work is scheduled to start on Nabucco in 2011. It is expected to cost about 10bn euros (£8.9bn; $13.4bn) and should supply up to 31bn cubic metres of natural gas annually - no more than 5% of EU gas needs.
The summit also considered plans for an Inter-Connector pipeline linking Turkey to Italy via Greece, and White Stream, which would run from Georgia to Romania via the Black Sea.