Pope John Paul II has inaugurated the newly-restored Sistine Chapel after 20 years of restoration work.

Some of the world's most famous and precious frescoes are contained in the chapel, where popes are traditionally elected.

It has taken restorers twice as long to renovate the 15th and 16th Century wall paintings, which were covered in soot and grime, as it took to paint them.

At the private inauguration ceremony, the Pope said: "This place is dear to the world's faithful, not only for the masterpieces it contains but also because of the role it plays in the life of the Church."

The restoration work has brought back to life colours that have been hidden for hundreds of years and experts say they should stay like that for decades.

To ensure that the effects are long-lasting, a special air-filtering system has been installed to remove some of the pollution that enters the chapel along with the millions of people who visit every year.

The last of the frescoes to be cleaned involved 12 that were painted in the 1400s at the chapel's second level.

They depict scenes from the life of Christ and the life of Moses, painted by artists such as Pietro Perugino, Sandro Botticelli, Luca Signorelli and Domenico Ghirlandaio.

The last phase of the restoration, which cost $3.1m, was approved in 1994 after the highly successful cleaning of the most famous frescoes - Michelangelo's ceiling paintings and his Last Judgement panel behind the altar.

The project began in 1979, when restorer Gianluigi Colalucci applied a new solvent to a postage-stamp-sized section of one of Michelangelo's frescoes.

If his experiment had failed, none of the subsequent work would have been carried out.

Cardinal Edmund Szoka, governor of Vatican City, said: "This restoration and the expertise of the restorers allows us to contemplate the paintings as if we had been given the chance of being present when they were first shown."

Building work began on the Sistine Chapel, which is inside the Vatican's Apostolic Palace, in 1368. It takes its present name from a restoration ordered by Pope Sixtus IV in 1477.

In 1506, Pope Julius II asked Michelangelo to redecorate much of the chapel. He completed the famous ceiling frescoes in 1512