A US citizen has been detained by North Korea as tension mounts between Pyongyang and Washington.

The totalitarian state announced yesterday that it had arrested a fourth US citizen raising fears that leader Kim Jong-un is attempting a new era of “hostage diplomacy”.

The detention of Kim Hak-song on suspicion of “hostile acts” against the North Korean regime follows that of lecturer Kim Sang-duck, also known as Tony Kim, who was arrested last month as he tried to leave the country.

The 55-year-old former professor at Yanbian University of Science and Technology in China had reportedly been working on humanitarian projects in North Korea. He is accused of plotting to “overturn” the government.

Kim Hak-song had been working at the Pyongyang University of Science and Technology (PUST) before he was arrested on Saturday. Founded in 2010, the university is funded by South Korean and US evangelical Christians and teaches the children belonging to North Korea’s elite. Two more US citizens, Kim Dong-Chul and Otto Warmbier, were sentenced last year to 10 years and 15 years hard labour respectively. The former was charged with spying, while Warmbier, a 22-year-old student at the University of Virginia, was detained for trying to take home a political banner he had removed from the wall of his hotel. He was detained as he was leaving North Korea with his tour group.

The detentions follow North Korean threats of a new nuclear test prompting the US to send a warship to the region. On Friday, Pyongyang accused South Korea and the US of planning to assassinate Kim Jong-un but has not otherwise responded to US President Donald Trump’s recent comment that he would be “honoured” to meet the dictator.

North Korea has previously detained US citizens to use as bargaining chips and analysts believe Kim Jong-un is using them to show defiance as well as lessen the likelihood of any attack being launched against the state.

“Kim Jong Un is using hostage diplomacy as a part of his military and defence strategy with focus on preventing the US from removing him from power as well as preventing the US from taking military options against North Korea,” said former defector Dr An Chan Il, president of the World Institute for North Korea Studies.

Dr Koh Yu Hwan, of Dongguk University in Seoul, said the situation showed Trump was being “played” by the North Korean leader.

“Although such hostage talks don’t usually lead to negotiation over missile or nuclear weapons ... the added numbers can certainly hamper and limit options the US can take over North Korea,” Koh said.

“Donald Trump is going to be played by Kim Jong-un who has handled this situation better than he has.”

John Nilsson-Wright, of the London-based Chatham House think tank, said: “The current situation is not a bad one for Kim Jong-un.

“He’s had a lot of airtime and the more he continues to test missiles and move forward with militarisation, he can demonstrate his independence to the international community and present himself to his people as unbowed.”

He added: “It’s poking a stick in Donald Trump’s eye in a signal of defiance.”

Last week US Secretary of State Rex Tillerson said the US was not seeking to change the regime although he has previously suggested that military action was “on the table”.

On Thursday the US House of Representative voted almost unanimously to tighten sanctions on North Korea and any countries that assist in its nuclear programmes.