Witnesses reported that truckloads of Rwandan soldiers recently crossed the border and were camped within 20 miles of Goma, which was captured last month and briefly occupied by a rebel force called the M23 movement. United Nations officials confirmed a sudden military buildup around Goma but said that they did not know the identities of the various groups of soldiers.
“It feels a bit like a boiling kettle, about to blow up,” said Thierry Goffeau, the leader of the mission in Goma for the aid organization Doctors Without Borders.
The M23 rebels are widely believed to be covertly armed by neighboring Rwanda, and in the past few months they have eviscerated the Congolese Army in just about every battle.
Aid workers in Goma said the Congolese Army had been reinforcing its positions in the last few days with tanks, heavy artillery and allies from some very unscrupulous militias.
Several Goma residents said that while businesses were open during the day, the city had become lawless at night, especially after hundreds of criminals, including militia leaders, escaped from a hole punched through the back wall of Goma’s central prison last month.
Outside Goma, the camps sheltering tens of thousands of displaced people were becoming the site of midnight attacks, with swarms of armed men flooding in.
Mr. Goffeau said the situation in Masisi, a highly fertile area north of Goma, where the M23 and other armed groups have been mobilizing, was becoming “very, very, tense.”
Eastern Congo has been mired in violence for more than 15 years, and it seems the capture of Goma last month has stirred up all sorts of tensions and rivalries that threaten the stability of this area and possibly of the vast Congo as a whole. “You have hundreds of tiny armed groups plying the countryside, making havoc,” said Jay Drosin, the director for the International Medical Corps’s program in Congo.
Mr. Drosin said the situation was “constantly fluid and extremely unpredictable” and “more uncontrollable than it’s ever been.”
Eastern Congo is blessed with gold, coltan, cassiterite and other minerals. These easy-to-move riches, along with longstanding ethnic tensions and a dysfunctional central government, have become a toxic brew that has killed countless Congolese.
Analysts say that the Congolese Army, in its desperation to fight off Rwandan-backed forces, has reactivated its alliance with the infamous Democratic Forces for the Liberation of Rwanda, known as the F.D.L.R., a militia blamed for burning down villages, massacring civilians and raping thousands of women.
The F.D.L.R. is commanded by ethnic Hutus and includes remnants of the force that committed genocide in Rwanda in 1994, when hundreds of thousands of ethnic Tutsis were hacked to death. Humanitarian groups said that in the last week, militia fighters, including from the F.D.L.R., as well as from another militia group known as the Mai-Mai, have infiltrated some of the displaced persons camps ringing Goma with the cooperation of the government’s army. Aid groups are worried that the militants may try to use the camps as a springboard to wage attacks against Tutsi-led Rwanda. This is what happened in the mid-1990s, setting into motion a series of events that culminated in Rwanda invading Congo and helping to topple its government.
“There are these young guys in the camps, very well dressed, that are definitely not displaced persons,” Mr. Goffeau said. “Something weird is going on.”
Many aid workers said ethnic tensions in the Goma area were increasing and could set off bloodletting between Hutus and Tutsis and other ethnic groups that may align themselves with either side.
Analysts said that Rwanda might sweep into Congo again if the Hutu militants around Goma actually mounted a serious incursion into Rwanda. But they also noted that Rwanda would be reluctant to go on the offensive while peace talks were under way in Uganda, which has been hosting representatives of the Congolese government and the M23 rebel group in the hopes of brokering some sort of truce. “We will be here if it takes a day, or a week, or a year,” Bertrand Bisimwa, a rebel spokesman, said Thursday from a hotel room in Kampala, Uganda.