Brazzaville - Police in southern Republic of Congo used violence and subjected illegal immigrants to degrading treatment in the second phase of a crackdown that drove thousands from the country last year, the Catholic Church and a local charity said on Sunday.
Congolese authorities on Thursday launched the next step in operation "Mbata ya bakolo" ("The slap of the elders" in the local Lingala language) in the economic hub of Pointe-Noire.
A similar drive in April 2014 forced an estimated 250 000 workers from neighbouring Democratic Republic of Congo back across the river in a few weeks.
Public radio reported that 600 foreigners had been arrested in just two days last week.
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The Catholic Church in Pointe-Noire and local rights charity RPDH said illegal immigrants were now the "subject of a full-blown manhunt by police," whom the UN has accused of numerous abuses during a similar sweep in the capital Brazzaville in April 2014.
"Many abuses or violations of human rights have been reported," the Church and RPDH said in a statement.
"These acts, contrary to the rules and principles of the rule of law, are notably characterised by intimidation and threats, violence, inhuman and degrading treatment as well as arbitrary arrests."
Police spokesman Jule Monkala Tchoumou had no immediate comment on the allegations.
The conflict-ridden DRC ranks last on the UN development index and over the years tens of thousands of its nationals have found menial jobs in neighbouring Congo, where living conditions are slightly better.
Official figures from Kinshasa in April showed around four million residents in Congo, equivalent to around one in 10 of the population, hailed from DRC.