Officials from the United Nations mission in Congo could not be reached for comment.

“This is the big escalation we’ve been expecting for months,” said Jason K. Stearns, an expert on eastern Congo and author of “Dancing in the Glory of Monsters,” a history of Congo. “But for the M23, taking Goma is a gamble. It gives them huge leverage, but also brings greater infamy.”

And, he added, “It will be a serious blow to the region’s stability.”

The M23 group is made up of soldiers from a former rebel army that signed a peace deal with the government on March 23, 2009, and was integrated into Congo’s national army. But last spring, hundreds of them mutinied, claiming that the government had failed to meet their demands under the 2009 agreement.

The figurehead of the group is believed to be Gen. Bosco Ntaganda, a former rebel and high-ranking army officer wanted by the International Criminal Court to answer charges that he committed war crimes and crimes against humanity.

The rebellion broke out as Congo and foreign governments called for the arrest of General Ntaganda. Since then, Rwanda and Uganda have been accused by a United Nations panel of experts of aiding the rebel movement, a charge that both countries deny.

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The violence has ebbed and flowed over the year, and many analysts see it as political posturing rather than an attempt to overthrow the government.

But a new wave of fighting erupted last week, with the army claiming to have killed more than 150 rebels and the rebels capturing the town of Kibumba, about 18 miles from Goma.

The forces of the United Nations mission in Congo bombed rebel positions on Saturday and Sunday, but that did not seem to blunt the rebels’ advance.

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After taking Kibumba, the rebels, who are said to be well equipped with arms and even night-vision goggles, sped down the main road southward toward Goma. By Sunday evening, they had reached Kibati, a refugee camp about two miles away.

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Witnesses in Kibati said that the camp, which had tens of thousands of displaced residents early Sunday, was empty by evening.

“We are still holding the airports,” said a Congolese Army spokesman, Olivier Hamuli. “Goma till now is not yet in rebel hands. And until now we are holding the line.”

Mr. Hamuli dismissed reports from Goma that said the Congolese Army had abandoned the city, saying that some troops were moving just for “relief,” and that the army was prepared to defend Goma if attacked.

The situation is reminiscent of the rebel offensive of 2008 that threatened Goma after a string of rapid military victories against the army. The rebels’ leader at the time, Laurent Nkunda, threatened to advance all the way to Congo’s capital, Kinshasa, and neighboring nations readied themselves for a regional war.

But Mr. Nkunda was arrested by Rwanda, which denied claims that it had been supporting him, just as it has denied that it is backing the current rebel leader, General Ntaganda.

After an emergency meeting over the weekend, the United Nations Security Council called for the rebels to halt their advance toward Goma, The Associated Press reported.