The problem is that the security environment has worsened."He added that the continuing actions of armed groups "calls for a stronger closely coordinated response, and we are working in a very coordinated manner with the Congolese security forces, but the adversary is a more hard adversary that knows the ground that is blending into the population".
The vaccination programme launches on Wednesday with support from the World Health Organization, targeting 2,000 frontline workers in districts close to DRC's North Kivu province, which is now experiencing an outbreak of the deadly virus.
Recently, the World Health Organization (WHO) said there is not enough valid research to risk the health of pregnant women nor their future child with the investigational vaccine rVSV-ZEBOV.
It is the first time an Ebola outbreak has occurred in DRC's far northeast, where multiple rebel groups are active. The United States - vitally important to the global response in West Africa 2014-2016 - has chosen thus far, out of security concerns, to limit its engagement to the periphery of the outbreak.
This story has been corrected to indicate the number of Ebola deaths in the current outbreak is 189, not 198.
Healthcare responders may consider vaccinating broader populations in place of the current vaccination strategy, which focuses on vaccinating people who have been exposed to Ebola patients.
Authorities insist vaccination will be totally voluntary and that frontline workers - who may include hospital cleaners and other auxilliary staff - would need to give "informed consent". The tactic helped eradicate smallpox in the 1970s.
Dozens of armed militias operate in the area, attacking government outposts and civilians, complicating the work of Ebola response teams and putting their security at risk.
For Congolese health workers, combating the virus has proved a challenge in a densely populated region that is roamed by armed groups.
Uganda has for the first time imitated a vaccination drive against Ebola Hemorrhagic Fever (EHF) as a preventive measure against the disease that has for the past months ravaged neighbours, DR Congo. In 2000 and 2001, 574 people were infected and 261 died in Uganda.
In the worst Ebola epidemic to date, the disease struck the West African states of Guinea, Liberia and Sierra Leone in 2013-15, killing more than 11,300 people.