The United States on Wednesday placed sanctions on three close associates of South Sudan's president, saying they had personally profited from a climate of corruption in a government that has been called a kleptocracy.

The Treasury Department imposed sanctions on Gen. Malek Reuben Riak Rengu, the army's deputy chief of staff in charge of military procurement; and Michael Makuei Lueth, South Sudan's information minister. In addition, sanctions were placed on Paul Malong Awan, who was chief of staff of the South Sudan People's Liberation Army until President Salva Kiir fired him in May. Three companies owned or controlled by Riak also were sanctioned.

The Treasury Department said the sanctions were in response to the deteriorating humanitarian situation in South Sudan and the role of officials in undermining stability and peace.

"These actions send a clear message to those enriching themselves at the expense of the South Sudanese people that we will not let them exploit the U.S. financial system to move and hide the proceeds of their corruption," said Sigal Mandelker, undersecretary for terrorism and financial intelligence. "Treasury will forcefully respond to the atrocities ongoing in South Sudan by targeting those who abuse human rights, seek to derail the peace process and obstruct reconciliation in South Sudan."

State Department spokeswoman Heather Nauert said in a statement that the Trump administration will increasingly scrutinize South Sudanese officials.

"This is a man-made crisis, and one the Government of South Sudan can stop," she said.

The sanctions come days after Kiir met in the capital of Juba with a senior U.S. official who raised concerns about the violence sweeping South Sudan and the dangers posed to humanitarian workers trying to reach starving people amid a civil war.

Mark Green, administrator of the U.S. Agency for International Development, said he warned Kiir that the administration is reviewing U.S. policy toward South Sudan, but Kiir dismissed all his concerns. The following day, after he visited U.N. and church compounds where tens of thousands of ethnic minorities have sought protection from government ­forces who have looted their homes and killed people, Green told reporters that he thought Kiir should visit the same sites and observe the truth firsthand.

[U.S. warns South Sudan: Chaos is not acceptable]

The timing of the sanctions so soon after Green's visit suggests that while the measures were already in the works, they could have been averted if Kiir had acknowledged the lawlessness and government corruption and agreed to improve the situation.

The United States has spent about $730 million this year on humanitarian aid to people uprooted by almost four years of conflict.

South Sudan is the newest and one of the poorest countries in the world. It declared independence from Sudan in 2011, and war erupted two years later over a falling-out between Kiir and his vice president, a political rival. Since then, 2 million civilians have been displaced inside South Sudan, and another 2 million have fled as refugees to neighboring countries. In the chaos engulfing the country, 83 humanitarian aid workers have been killed, making it the most dangerous place in the world for them to work.

In 2014, President Barack Obama placed sanctions on six military officers in South Sudan, including one who commands opposition troops. None ranked as high or was as closely linked to Kiir as those sanctioned Wednesday.

Officials from the United Nations and donor countries have visited South Sudan recently to urge Kiir to participate in peace negotiations. Almost all have said the government is as much to blame for the violence and resulting famine as the opposition troops fighting it.

A report last year in the Sentry, an investigative group funded by actor George Clooney, said top officials in South Sudan have accumulated fortunes while war and atrocities have pushed the country to the edge of collapse. The State Department's latest human rights report cited the Sentry's conclusion that South Sudan's government is a kleptocracy.

The Treasury Department said Riak was responsible for planning offensives in which civilians were targeted and human rights abuses occurred. It said he had entered into contracts with inflated ­prices, for which he received kickbacks.

According to the Treasury Department, Malong ordered army units to block the movement of humanitarian supplies for hungry civilians, claiming that food would be diverted to militias instead. Treasury said that after Malong was fired and fled Juba, he was reportedly stopped carrying millions of U.S. dollars allegedly stolen from the army.

Makuei, as information minister, was accused of advocating actions that obstructed the delivery of humanitarian aid. Last week, Makuei said in a news conference that the government will review the mandate for U.N. peacekeepers to operate in South Sudan when it is scheduled for renewal in December.