He also added that "the parties of the centre-left coalition must respect the general interest of the government's common action, and must respect and follow the [government's] programme."
The remarks were made as Prodi opened a senate debate that will conclude with a confidence vote on his government on Wednesday night.
He also promised a reform of the electoral system that has been blamed for contributing to political instability by giving too much influence to small parties.
Prodi acknowledged that there were differing opinions on Afghanistan, but said there was awareness that a military presence could not be the only solution.
"The goal of our presence in Afghanistan is to consolidate democratic institutions," Prodi said.
"Our soldiers bring a culture of dialogue and help, not of clashes."
Prodi stressed that his government had sought to raise its profile in Europe while maintaining good relations with Washington. But he said that it had not gone as far as the friendship pursued by Silvio Berlusconi, his predecessor.