The comments by Jeff Bleich, the U.S. ambassador to Australia, to the Australian news program "Q&A" on Monday came barely two weeks after the U.S. State Department expressed concern about the online restrictions, which would make Australia one of the strictest Internet regulators among the world's democracies.
The Internet needs to be free," Bleich said. "We have been able to accomplish the goals that Australia has described, which is to capture and prosecute child pornographers ... without having to use Internet filters."
Bleich said Washington was sharing with Canberra other methods of combating illegal content.
Australian Communications Minister Stephen Conroy says the filter would block access to sites that include child pornography, sexual violence and detailed instructions in crime or drug use.
The plan needs the support of Parliament to become law later this year. Some critics of Australia's proposed filter have said it puts the nation in the same censorship league as China, and Internet giants Google and Yahoo have criticized the plan as heavy-handed.
The U.S. State Department said last month that open Internet access encouraged economic prosperity and the free flow of information.