The European Commission on Tuesday gave Bulgaria and Romania the go-ahead to join the European Union in January, but with the closest monitoring system ever imposed on new members.

The 26th and 27th members of the European club will be allowed to join up on January 1, 2007, Commission President Jose Manuel Durao Barroso announced at an plenary session of the European Parliament in Strasbourg.

"I would like to congratulate the peoples and the authorities of Bulgaria and Romania for all the efforts they have produced in order to fulfil the conditions for accession to the European Union," said Barroso.

In a report to the assembly, the Commission -- the EU's executive arm -- decided not to recommend that membership be pushed back by a year, as it was empowered to do, but set out a number of measures to ensure the two new members comply with EU standards.

Among the areas of concern to be closely monitored are corruption and crime and food safety.

Romanian President Traian Basescu voiced his delight but warned: "Our life will not change in a fundamental manner between December 31 and January 1... Prosperity won't follow automatically."

Bulgarian Foreign Minister Ivaylo Kalfin also hailed the decision but recognised that work remained to be done.

"The accession is an enormous achievement but we have to be aware that after January 1, 2007, it will be even more difficult for us as we need to continue reforms in the judiciary (and that) corruption, wrongdoings and crime are beyond the pale," he told national radio.

While it was good news for Sofia and Bucharest, the decision was less encouraging for the EU candidate nations queueing up to join the club, including Croatia, Macedonia and Turkey.

"With Romania and Bulgaria's adhesion, I think that an institutional agreement should precede any more enlargement," said Barroso.

That would mean in some way re-heating the moribund EU constitution, or at least its main planks, which suffered two stunning reversals last year when French and Dutch voters rejected in a referendum in each country.

Top officials in Macedonia and Croatia nevertheless said they remained optimistic about their countries' prospects of joining the bloc.

A senior Turkish diplomat meanwhile said Ankara would reject any bid to impose tougher conditions on its own struggling bid to join the EU.

Amid weakening support for further enlargement and fears of a flood of new job-seeking migrants, most member states are expected to impose restrictions to workers from the two newcomers, as they did when 10 mainly former Soviet-bloc countries joined in 2004.

Moreover, "safeguard mechanisms of last resort" may be applied to Bulgaria and Romania for up to three years after they join.

They include the possibility of withholding EU funding, the temporary suspension of EU rights, banning the sale of unsafe food and the non-recognition of certain civil and criminal judgements or arrest warrants.

Both new members will have to report to the Commission twice a year on the benchmarks that are to be met, with the first report due by March 31, 2007.

The safeguard measures will "reassure Eurosceptics that the EU won't just accept whatever happens," said Lucia Montanaro-Jankovski, an analyst at the Brussels-based European Policy Centre.

Welcoming the green light to the newcomers, the Czech foreign affairs minister praised the safeguards as "an impulsion for the two countries to complete as quickly as possible their preparation in the sectors were certain deficiencies have been observed."

Britain also hailed Tuesday's decision but warned it would only gradually open access to immigrants from the two new countries. Britain had been one of only three countries not to restrict immigration from the 10 countries that joined in 2004.

Bulgaria and Romania will be among the poorest members of the EU, making up six percent of the bloc's population but less than one percent of its gross domestic product (GDP).

In both countries, GDP per head is about a third of the EU average, but growing rapidly.

Adding Bulgaria and Romania to the European club will give the EU a new neighbour, Moldova, and bring the bloc's total population to some 487 million.