PORT-AU-PRINCE / WASHINGTON (REUTERS) - The United States is still reviewing a request for troops made by Haiti's interim Prime Minister Claude Joseph to help secure its airport and other infrastructure after the assassination of President Jovenel Moise, the White House said on Monday (July 12).

White House press secretary Jen Psaki said Haiti's political leadership remains unclear and that it was vital for the country's leaders to come together to chart a united path forward.

"It's still under review," she said of Haiti's request to send troops. Asked if it had been ruled out, Ms Psaki said, "No."

US. President Joe Biden told reporters later on Monday that his administration was "closely watching" developments in Haiti.

"The people of Haiti deserve peace and security, and Haiti's political leaders need to come together for the good of their country," Mr Biden said.

Mr Moise was shot dead early on Wednesday at his Port-au-Prince home by what Haitian authorities describe as a unit of assassins including 26 Colombians and two Haitian-Americans. Haitian police said on Sunday they had arrested another suspect.

A separate US government source said on Monday that at least one of the Haitian-Americans arrested on suspicion of taking part in Mr Moise's killing had been an informant for the US government law enforcement agency.

The death of the president plunged the troubled country into deeper turmoil, and US officials travelled there on Sunday to assess the situation and meet three politicians who have all staked competing claims to take charge.

"What was clear about their trip is that there is a lack of clarity about the future of political leadership," Ms Psaki said at a news briefing.

Haitians in the capital Port-au-Prince were planning protests this week against Mr Joseph, according to social media posts. Mr Joseph's right to lead the country has been challenged by two other senior politicians, Prime Minister-Designate Ariel Henry and Senate President Joseph Lambert.

The political turmoil could worsen longstanding poverty and lawlessness for most Haitians if the acting government only focuses on the investigation into Mr Moise's killers, said Mr Feckenson Cheri, 33, who lives with his aunt in the capital.

"I know they're arresting the people they think killed the president, but I'm not sure they'll ever figure it out. What we need is help to save us from the misery that's all around us," he said.

Ms Emily Horne, a spokesperson for the US National Security Council, said the US delegation held a joint meeting with Mr Joseph and Mr Henry, and a meeting with Mr Lambert to "encourage open and constructive dialogue" to reach an agreement to enable Haiti to hold free and fair elections.

On Sunday, Haitian police said they had detained a suspected plot mastermind, 63-year-old Christian Emmanuel Sanon, widely described as a Florida-based doctor, whom authorities accuse of hiring mercenaries to oust and replace Mr Moise.

On Monday, Haitian police issued an arrest warrant for a Colombian, apparently in connection with the alleged plot. Colombian media said the man was a retired soldier.

Colombian police said on Monday they could not share any hypothesis about the death of Mr Moise and that they respect the Haitian state's autonomy. So far 18 Colombians tied to the case have been arrested and three more killed.

Families of some of the Colombians, many ex-soldiers, have said their relatives were hired as bodyguards, not as mercenaries, and that they did not kill Mr Moise.

The men were initially contracted to protect Mr Sanon and were later presented with a warrant to arrest Mr Moise, Haiti's National Police Chief Leon Charles said Sunday.

Photos said to be of Mr Sanon meeting with a group of men, including another suspect in the case, Haitian-American James Solages, began circulating on social media late on Sunday.

Reuters could not verify the authenticity of the images.

A man by Mr Sanon's name is listed online as a doctor who has worked in Florida, where a security company that Haitian authorities say hired suspects in the case is based.

High-ranking Colombian intelligence officials have been in Haiti since Friday to assist with the investigation.