North Korean leader Kim Jong-un's sister Yo-jong arrived in Vladivostok, Russia on Monday ahead of her brother's arrival for a summit with Russian President Vladimir Putin later this week.

"Kim Yo-jong boarded a flight in Pyongyang for Vladivostok in the morning," a source said. "She flew to Russia ahead of Kim Jong-un to prepare for the summit."

In Vladivostok, Kim Yo-jong was briefed by Kim Jong-un's head of protocol Kim Chang-son, who was already there. On Sunday, Kim Chang-son inspected the potential site of the summit, the Far Eastern Federal University on Russky Island off Vladivostok.

Kim Jong-un is expected to depart Pyongyang on a train on Tuesday and arrive in Vladivostok on Wednesday. The 700-km journey takes about 10-15 hours.

Kim will likely ask for help from Putin after a summit with U.S. President Donald Trump in February collapsed without easing international sanctions.

