President Kabila was due to step down in December 2016, but Congo failed to organize elections, leading to deadly protests.
Two United Nations experts, including an American, were killed in Congo in March, but a local inquiry has been criticised.
Moise Katumbi, the chairman of Congo's premier football team and a presidential candidate, has not set foot in the country for a year.
Buying a passport in Congo costs $185, almost half a citizen's annual income.
President Joseph Kabila is due to step down when the next elections are held.
Etienne Tshisekedi, the longtime opposition leader, died in February.
Etienne Tshisekedi was the man with the experience to lead Congo to elections in 2017. After his death, they are in doubt.
At least 34 people in Congo have been killed in protests since Monday, a human-rights researcher has claimed.
Scores of anti-Kabila protesters were killed in recent clashes with security forces.
The Congolese government has expelled several foreign researchers already in 2016.