By Joe Bavier
KINSHASA, Oct 26 (Reuters) - Congolese rebels launched a new offensive on Sunday, defying the U.N. Security Council and for the first time seizing the headquarters of a park that is home to many of the world's last mountain gorillas, officials said.
The U.N. Security Council condemned Congolese Tutsi rebel leader Laurent Nkunda last week for calling for a national rebellion, and urged all armed groups in the huge country's violent eastern provinces to lay down their arms.
Nkunda's fighters accuse Congo's army of attacking them, and say the U.N.'s biggest peacekeeping mission has sided with the army and Rwandan Hutu rebels.
Nkunda's forces drove government troops out of an army base at Rumangabo, North Kivu province, during intense fighting early on Sunday, and heavy artillery exchanges were continuing, a spokeswoman for the U.N. mission, MONUC, said.
Virunga National Park authorities said the rebels had seized its headquarters 5 km (3 miles) away at the same time.
"When the rebels started approaching the park station we thought we were all going to be killed," Park Ranger Bareke Sekibibi was quoted as saying in a statement issued by the park.
Virunga, near the border with Uganda and Rwanda, is home to around 200 of the world's 700 remaining mountain gorillas.
"The conflict on the ground is chaotic and dangerous and we cannot allow our rangers to become targets," Virunga Director Emmanuel de Merode said in the statement.
The rangers were walking through the forest to Kibumba, 20 km (12 miles) south of Rumangabo, from where trucks would evacuate them to the provincial capital Goma, de Merode said.
Nkunda's fighters briefly overran the army base at Rumangabo earlier this month in an offensive that prompted accusations from Congo's government that neighbouring Rwanda's Tutsi-led government had sent troops to help Nkunda's campaign.
Rwanda denies the accusations.
U.N. REINFORCES POSITIONS Heavy artillery exchanges continued on Sunday around Rugari, about 5 km (3 miles) south of Rumangabo on the main road between Goma and Rutshuru town to the north.
"The CNDP have retaken control of Rumangabo ... we have reinforced our detachments to prevent the fighting spreading," said MONUC's North Kivu spokeswoman Silvie Van Den Wildenberg.
Nkunda's rebels said they were responding to Congolese army (FARDC) attacks on their positions in North Kivu in recent days.
"If MONUC was not going to stop the FARDC offensive, they should not stop our counter-attack," said Bertrand Bisimwa, a CNDP spokesman.
"We have no alternative but to continue fighting. Wherever we are shot at from, whether it is Kibumba or Goma, we will go," he said. "MONUC should stop messing with us."
Bisimwa said CNDP fighters were also fighting in the Tongo area, where they fought a heavy two-day battle with the army in mid-October. MONUC military sources could not confirm the fighting there, or in the other places where Bisimwa said the army had attacked the rebels in recent days.
Around 100,000 civilians have fled their homes in North Kivu since a January peace deal collapsed in August. Congo's 1998-2003 war and resulting humanitarian disaster have killed an estimated 5.4 million people, most through hunger and disease.
(Writing by Alistair Thomson; editing by Andrew Roche)