Under North Korea's criminal code, conviction for illegal entry could mean up to three years in a labor camp.
Espionage or "hostility toward North Koreans" - possible crimes that could be considered "hostile acts" - could mean five to 10 years in prison, according to South Korean officials.
The journalists, who work for San Francisco-based Current TV, a media venture founded by former Vice President Al Gore, were detained on March 17 near the border while reporting on refugees living in China.
Friday's announcement follows the release of a U.S. journalist who had been imprisoned in Iran for four months after an appeals court reduced her original eight-year prison sentence to a two-year suspended sentence.
North Korea's detention of the American reporters come amid mounting diplomatic tensions between Pyongyang and Washington over the North's moves to restart its nuclear program following its April 5 rocket launch.
Angered by international criticism of the launch, the North has quit international nuclear talks, expelled inspectors and threatened to conduct nuclear and long-range missile tests.
Pyongyang claims the launch put a satellite into orbit, but other nations believe it was a long-range missile test.
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