U.S. President Donald Trump added to speculation that North Korea may make a goodwill gesture before his planned summit with leader Kim Jong Un when he tweeted of a possible update soon on the status of three detained Americans. Here's a brief look at those U.S. citizens:

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KIM DONG CHUL

Kim, a South Korean-born U.S. citizen, has been held the longest. The former Virginia resident was sentenced in April 2016 to 10 years in prison with hard labor after being convicted of espionage. He reportedly ran a trade and hotel service company in Rason, a special economic zone on North Korea's border with Russia.

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KIM HAK SONG

Kim worked in agricultural development at an experimental farm run by the Pyongyang University of Science and Technology. The university is the only privately funded college in North Korea and was founded in 2010 with donations from Christian groups. He was detained last May for alleged anti-state activities.

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TONY KIM

Tony Kim, who also uses the name Kim Sang-duk, was detained a year ago at the Pyongyang airport. He taught accounting at the Pyongyang University of Science and Technology. He was accused of committing unspecified criminal acts intended to overthrow the government.