European Central Bank (ECB) President Jean-Claude Trichet congratulated Slovenia for a successful changeover to the euro but urged authorities to step up efforts to match economic gains elsewhere in the European Union.

"Not only did Slovenia perform exceptionally well in its convergence process to the euro area, but the last bit, the cash changeover was also exemplary so far," Trichet said when addressing a conference organized in capital Ljubljana to celebrate the end of the changeover to the euro.

Slovenia on January 1 became the 13th member of the eurozone and the first former communist state to join the single currency.

Several European heads of government are attending the Ljubljana celebrations, including German Chancellor Angela Merkel, whose country currently holds the European union presidency.

Sunday was the last day tolars could be used in shops around the country. From Monday, some two million Slovenians have to first change their old currency into euros at the bank.

A dual circulation period lasting two weeks began on January 1, during which retailers and service providers had to accept all bills and payments in both tolars and euros, although they were obliged to give change exclusively in euros.

"My message to the Slovenian economy and executive branches is to continue working very seriously in order to permit the catching up process to continue and be as successful as it has been in the past," Trichet said.

European Commission's President Jose Manuel Barroso said Slovenia's adoption of the euro was an important historic step for Slovenia but warned Slovenians not to "ask the euro to deliver what only structural reforms can help us to achieve: higher growth."

"The euro not only brings huge benefits, but also important responsibilities in terms of maintaining macroeconomic stability and Slovenia's competitiveness in a single currency environment," Barroso said addressing the conference organized to celebrate the end of the euro changeover.

European Economic and Monetary Affairs Commissioner Joaquin Almunia said Slovenia had achieved striking economic policy successes and would benefit from the eurozone by increasing its economic stability, lowering interest rates and transaction costs and getting better protection against external shocks.

"But further efforts are also required," Almunia warned Ljubljana, in reference to two key policy considerations after it joined the eurozone.

"The need to keep inflation low and safeguard competitiveness and the need to guarantee the long term sustainability of public finances," Almunia said.

He added the commission was concerned over expectations that Slovenia's average old-age dependency ratio would more than double by 2050 placing the long term sustainibility of the tiny Alpine state's finances in the "high risk" category.

European Union and ECB officials also warned against the unjustified rounding-up of prices that was registered over the last months in Slovenia.

"Citizens in Slovenia play a very important role here: the consumers in a market economy have a major influence on price formation... they will be a major force in preventing any unjustified price increases," Trichet maintained.

Slovenia registered a 2.8 percent 12-month inflation in 2007 with prices increasing by 0.4 percent in December from the previous month.

"There was no objective justification for the December price increases registered in restaurants," Slovenia's Statistical Office said in a statement last week after analysing the main causes of December's inflation.

Slovenian central bank governor Mitja Gaspari said the bank was being very cautious over some price hikes which he tought were only short-term ones.

"We (the central bank) should be in alert, ready to act if such process (of price increases) would continue," Gaspari said.

Slovenian Financial Minister Andrej Bajuk said the big-bang changeover, which brought a simultaneous switch of financial transactions and cash payments from tolars into euros, had "run as planned."

"We should now be aware this is not the end of our path, its an important step towards our common European home but it brings new challenges," Bajuk said.