Congolese tanks and thousands of displaced people enter Goma in eastern Congo on Wednesday. Thousands of refugees started streaming into the eastern provincial capital of Goma in the afternoon, impeded by army tanks, trucks and jeeps pulling back from the battle front.

Goma, Congo ? Firing wildly, Congolese soldiers commandeered cars, taxis and motorbikes Wednesday in a retreat from advancing rebel fighters, joining tens of thousands of terrified refugees struggling to stay ahead of the violence.

As gunfire crackled in this eastern provincial capital, the Tutsi rebels said they had reached the outskirts of Goma and declared a unilateral cease-fire to prevent panic as the army retreats and residents flee.

Congo said Rwandan troops had crossed the border and attacked its soldiers – raising the specter that neighboring nations will again be drawn into Congo’s war. Rwanda’s Tutsi-led government immediately denied the charge, but Congo turned to Angola for help defending its territory.

As the chaos mounted, the U.S. announced its officials were leaving Goma and urged all American citizens to do the same. The State Department said Assistant Secretary of State for African Affairs Jendayi Frazer was heading to the capital, Kinshasa, and would arrive Thursday.

“There is a lot of violence,” said spokesman Sean McCormack. “This is of deep concern to us.”

Thousands of panicked refugees clogged the dirt roads out of Goma, struggling to reach safety.

Women carrying huge bundles on their heads and babies in their arms trudged alongside men pushing crude wooden carts crammed with clothing, food and cooking utensils. Bewildered children walked alongside. Young boys led goats and pigs on tethers as men on bicycles weaved in and out.

The U.N. High Commissioner for Refugees said about 45,000 people fled the nearby village of Kibati, where they had been sleeping in a makeshift camp in the open air, in a matter of hours on Wednesday.

“It was very chaotic,” said agency spokesman Ron Redmond, speaking from Geneva. Most refugees had arrived only the day before after fleeing fighting farther north.

“They suddenly became very agitated and people began leaving the camp in a panic,” Redmond said. They first headed toward Goma to the south, then changed direction and headed back out as it became clear the city was about to fall.

Goma’s governor, Julien Mpaluku, acknowledged that panic was spreading, but stressed that U.N. peacekeepers were still in charge and rebels had not yet entered the city. U.N. spokesman Madnodje Mounoubai said peacekeepers were deployed at the airport and at other strategic points.

A rebel statement said their fighters were just outside Goma.

“We are not far from Goma,” rebel leader Laurent Nkunda was quoted as saying on the BBC’s Web site. “But because there is a state of destabilization in the town we decided … unilaterally to proclaim a cease-fire.”

Nkunda, who has ignored calls by the Security Council to respect a U.N.-brokered truce signed in January, called on government forces to follow suit.

The U.N. says its biggest peacekeeping mission – a 17,000-strong force – is now stretched to the limit with the surge in fighting and needs more troops quickly.

The unrest in eastern Congo has been fueled by festering hatreds left over from the 1994 Rwandan genocide, in which half a million Tutsis were slaughtered. More than a million Hutu extremists fled to Congo where they regrouped in a brutal militia that helps fuel the continuing conflict in Congo.