"We are not concerned about chasing after North Korea and offering concessions to North Korea," she said.

But she said the US intends "to have an open door for a return to the six-party talks", referring to talks among the two Koreas, China, Japan, Russia and the US on ending the North's nuclear programme.

"We are not concerned about chasing after North Korea and offering concessions to North Korea"

Hillary Clinton, 
US secretary of state

"The ball is in the North Korean court," she said, adding that the North Koreans "know what their obligations are".

Ling and Lee, of US media outlet Current TV, were arrested along the North Korea-China border in March and accused of illegally entering North Korea with "hostile" intent.

North Korea has set June 4 as the trial date for the reporters who were working on a story about fleeing North Korean refugees when they were detained.

Clinton had earlier dismissed the charges against the two reporters as "baseless".

Bargaining chip

Analysts say the North is using the two journalists as a bargaining chip.

"As Iran did, North Korea may try and release them through diplomatic contacts," Cheong Seong-chang of Seoul's Sejong Institute think-tank, said.

Ling, left, and Lee are accused of illegally entering North Korea [EPA]
Earlier in the week, North Korean ally Iran released Roxana Saberi, a US-born journalist, after an Iranian appeal court reduced her jail sentence for spying.

"North Korea may use such contacts for discussion on pending issues and demand Washington ease sanctions. It has been using the case as a bargaining chip," Cheong said.

Yang Moo-jin, a professor at Seoul's University of North Korean Studies, said the North is likely to impose severe punishment on Lee and Ling.

"They are undergoing procedures similar to what happened to the US journalist held in Iran," he told AFP.

"Following the sentencing they might be pardoned, depending on the outcome of possible negotiations with Washington."

North Korea launched a rocket on April 5 that it said placed a satellite in orbit.

But the launch was widely believed to be a cover for a long-range ballistic missile test and drew international condemnation, including from the UN.

North Korea responded to the rebuke by pulling out of six-party denuclearisation talks, expelling inspectors and declaring that it would restart all its nuclear facilities.

It also threatened a fresh nuclear test unless the UN Security Council apologised for its rebuke.