Sixty-six inmates have perished in a packed prison in the Democratic Republic of Congo's capital this year already, a rights group said Monday, with some suffocating to death.

Emmanuel Cole, the head of a prisoners' rights body in the central African country, said two inmates had died in Kinshasa's Makala prison on Sunday.

"I myself saw their bodies," he said, adding that his organisation had recorded a total of 35 deaths in February alone.

Thirty-one inmates also died at the facility during January, according to Cole, who blamed the fatalities on poor nutrition, healthcare, and in some cases, suffocation inside tightly packed cells.

Makala prison -- Kinshasa's largest -- has an intended capacity of some 1,500 prisoners but currently houses about 11,000, Cole said. Some 7,000 of the inmates are in pre-trial detention.

Rights groups have regularly criticised harrowing conditions in Makala.

The DR Congo is one of the poorest countries in the world, despite having abundant reserves of minerals such as copper, cobalt and tin.