Mr Bush urged Italians to learn the "first-hand truth about America"
US President George W Bush has denounced "misinformation and propaganda" which he says are sullying his country's image abroad.
On a visit to Italy, he told young entrepreneurs on an exchange programme that going to the US would show them it was compassionate and open.
Mr Bush also held talks in Rome with Prime Minister Silvio Berlusconi.
The two leaders discussed the role of Italian troops in Afghanistan and further sanctions against Iran.
Mr Berlusconi offered his country's "inside knowledge" to help in talks aimed at persuading Tehran to abandon uranium enrichment. Italy has recently become the Iranians' largest European trading partner.
"Our offer is based on the fact that we know Iran very well from the inside - we have some leading companies that are operating there," Mr Berlusconi said.
In return for this co-operation, Italy wants US support in its bid to join the group of five permanent UN Security Council members plus Germany, which has been conducting negotiations with Iran.
Mr Bush meanwhile repeated a warning to Iran that it would face additional sanctions if it continued to defy the international community.
He said that diplomatic pressure remained the best path to deal with the issue, but again stressed that "all options are on the table".
'Misinformation and propaganda'
Mr Berlusconi has remained one of Mr Bush's staunchest allies in Europe
Security for President Bush's two-day visit has been very tight.
Commercial flights over the city have been diverted, 10,000 policemen have been mobilised, there are frogmen under bridges and snipers on roofs, and mobile phone signals are being disrupted whenever his motorcade moves, says the BBC's Christian Fraser in Rome.
As Air Force One touched down, hundreds were gathering in the city centre in protest at the Bush administration and Italy's involvement in Afghanistan.
Another group of demonstrators chanted "Bush, go home" outside the American Academy in Rome's Villa Aurelia while the president met young entrepreneurs inside.
HAVE YOUR SAY
One trip to Europe cannot make up for eight years of destructive foreign policy
CB, New York, US
Mr Bush urged them to ignore the "misinformation and propaganda" spread about his country and to learn the "first-hand truth about America" by visiting.
"The best diplomacy for America, particularly among young folks, is to welcome you to our country," he said.
"We are compassionate, we're an open country, we care about people and we're entrepreneurial."
Mr Bush will conclude his visit to Italy on Friday by meeting Pope Benedict XVI. In an unusual break with protocol, they will meet not in the Papal Study, but in the Vatican's gardens.
The Holy See said the Pope wanted to show his gratitude for the hospitality shown to him on his recent visit to the US. Afterwards, Mr Bush will travel to France and the UK.