Rebels in the Democratic Republic of Congo have taken control of large parts of the Virunga National Park, home to rare mountain gorillas.
Nine gorillas have been killed this year
The move has raised fears for the fate of the gorillas. Only 700 remain - half of which are in Virunga.
Meanwhile, the army says it has killed at least 28 troops loyal to rebel General Laurent Nkunda in the latest fighting in eastern DR Congo.
Some 170,000 people have fled the area this year, says the UN refugee agency.
"If anything happens to the mountain gorillas now, there is nothing we can do," said Norbert Mushenzi of the Congolese Institute for the Conservation of Nature (ICCN).
"As of today, the sector is no longer under my control and we have been rendered powerless by these actions."
Nine gorillas have been killed this year, allegedly by Gen Nkunda's men, sparking outrage among conservationists.
'State of war'
Gen Nkunda's forces are believed to have moved into the park in pursuit of Rwandan Hutu rebels, who have bases there.
Officials from local conservation group, Wildlife Direct, say the forces looted weapons and communication equipment from Jomba and Bikenge ranger patrol posts within the park.
A third post, Bukima, was being evacuated for fear of imminent attack, the group said.
Gen Nkunda, a Tutsi, has accused the government of forming an alliance against him with the Hutu FDLR, accused of involvement in the 1994 Rwandan genocide of Tutsis.
After Tutsis took control in Rwanda, they crossed the border into eastern DR Congo.
Over the weekend, Gen Nkunda told the BBC there was a "state of war" in North Kivu.
The United Nations says up to 10,000 people have fled fighting into Uganda.
The UN refugee agency says it is organising shelter for those who fled the violence Monday night and wish to stay on the Ugandan side of the frontier.
Following a visit by Rwandan Foreign Minister Charles Murigande to Kinshasa, DR Congo has promised to increase its operations against the FDLR.
Rwanda has twice invaded its large neighbour, saying it is trying to stop the FDLR from attacking its territory.
BBC Kinshasa correspondent Arnaud Zajtman says that the two countries are still divided by the same issues - DR Congo wants Rwanda to reign in Tutsi fighters, such as Gen Nkunda, while Rwanda wants DR Congo to stop the activities of the Hutu rebels, known as the FDLR.
Last month, Rwanda protested against DR Congo's move to call off an offensive against the FDLR.
Gen Nkunda says he is protecting ethnic Tutsis
Mr Murigande and his Congolese counterpart Mbusa Nyamwisi also asked the UN to intensify patrols in the east of the country where fighting is raging.
The UN has some 17,000 peacekeepers in DR Congo - the largest such force in the world and has sent an extra 200 troops to the region after the latest fighting.
Our reporter says the ministers have also agreed to form a commission to ensure that Congolese ethnic Tutsis who are refugees in Rwanda are repatriated.