Kenya's President William Ruto bid a ceremonial goodbye on Monday to some 400 police officers set to lead a UN-backed mission to tackle gang violence in Haiti, a government official and police source said.

The East African nation offered to send 1,000 police to stabilise Haiti, alongside forces from several other countries, but the deployment has run into persistent legal troubles.

However, Ruto has been an enthusiastic backer of the mission, and officials said over the weekend that a contingent would depart on Tuesday.

"This was an official flag off ceremony by the President. 400 officers are now ready to depart for Haiti tomorrow," an interior minister official told AFP.

A senior police officer said the president "handed over a Kenyan national flag" to the group.

He said the initial batch would be composed of elite officers from the Rapid Deployment Unit, General Service Unit, Administration Police, and Kenya Police.

"They have all undertaken a rigorous training for this exercise on top of their prior training of handling complex situations and are ready for the mission," he said.

"Please let's not doubt their capacity."

The deployment was approved by a UN Security Council resolution in October, only to be delayed by a Kenyan court decision in January.

The court said Ruto's administration had no authority to send officers abroad without a prior bilateral agreement.

While the government secured that agreement with Haiti in March, a small opposition party filed a fresh lawsuit in another attempt to block it.

Other countries that have expressed willingness to join the mission include Benin, the Bahamas, Bangladesh, Barbados, and Chad.

And while the United States is supplying funding and logistical support, Washington has made it clear there will be no US boots on the ground in Haiti, the poorest nation in the Americas.

Global monitor Human Rights Watch has raised concerns about the mission and doubts over its funding.

Watchdogs have repeatedly accused Kenyan police of using excessive force and carrying out unlawful killings.

Haiti has long been rocked by gang violence, but the recent surge has affected food security and humanitarian aid access, with much of the city in the hands of gangs accused of abuses including murder, rape, looting and kidnappings.