Earlier reports had suggested the two might have been seized after North Korean border guards crossed into Chinese territory.
The planned trial comes amid tensions between Pyongyang, regional countries and the wider international community over the North's rocket launch in early April.
Pyongyang said it put a communications satellite into space, but the US, South Korea and Japan believe it is was a long-range ballistic missile test.
Separately, Sergey Lavrov, the Russian foreign minister, arrived in Pyongyang on Thursday in an attempt to try to persuade the North to rejoin talks over its nuclear programme.
| Lavrov said he was not expecting a breakthrough during talks in Pyongyang [AFP]
Last week, North Korea expelled all international monitors from its nuclear facilities.
It vowed to restart its programme and quit disarmament talks, after the UN Security Council condemned its April 5 rocket launch.
Media reports have said Lavrov's trip could also include a meeting with Kim Jong-Il, the North Korean leader.
However, Lavrov said he was not anticipating a breakthrough.
"It is a difficult, difficult question. But it would be wrong to yield to emotions," he told reporters after talks with Pak Ui Chun, the North's foreign minister.
"We should concentrate on the structure that we already have. If everybody keeps this position, I believe, we could overcome this crisis."
North Korea's relations with Moscow are not as close as they were during the Soviet era but remain cordial.
Moscow usually avoids openly criticising the North.