JUBA (Reuters) - The United States has imposed sanctions on five South Sudanese officials it says are responsible for the likely murders of two human rights activists in 2017, as Washington piles more pressure on the war-torn country’s government.

The U.S. Treasury named Abud Stephen Thiongkol, Malual Dhal Muorwel, Michael Kuajien, John Top Lam and Angelo Kuot Garang as responsible for the disappearance and alleged killing of human rights lawyer Dong Samuel Luak and opposition politician Aggrey Idri in January 2017.

“Although the Government of South Sudan has denied knowledge of their whereabouts, multiple sources have stated that Dong and Aggrey were extraterritorially kidnapped in Kenya by members of the South Sudanese security services,” the Treasury said in a statement late on Tuesday.

A United Nations panel of experts reported in April that multiple credible sources suggested Aggrey and Dong were likely killed by South Sudan’s National Security Service.

The two government critics were in exile in Kenya but the U.N. panel alleged they were kidnapped by South Sudanese security service officers, flown back to Juba, and executed on a farm owned by President Salva Kiir. The government denied any involvement in their disappearance.

Deputy foreign affairs minister Deng Dau Deng told Reuters on Wednesday that the government would respond soon to the sanctions announcement.

The sanctions were just one step toward accountability for the deaths of Aggrey and Dong, the U.S. watchdog group The Sentry said on Tuesday. “Real justice will require the perpetrators of these crimes to be tried in a court of law,” it said.

President Kiir and opposition leader Riek Machar signed a peace deal in September 2018 to form the unity government by Nov 12. But days before the deadline, the two leaders gave themselves an extension of 100 days to implement the agreement, a move criticized by Washington.

Later last month, the U.S. recalled its ambassador from South Sudan and said it was re-evaluating its relationship with the South Sudan government.

Civl war broke out in oil-producing South Sudan in 2013, less than two years after the country gained independence from Sudan following decades of war. The conflict that has killed an estimated 400,000 people and forced millions from their homes.