PHNOM PENH, Cambodia (AP) _ Tanks and armored personnel carriers rumbled through Phnom Penh's streets Sunday on the second day of an apparent coup attempt by one of Cambodia's two feuding co-premiers. Residents awoke to the sound of shelling and gunfire in the northwest of the capital.

By midmorning, telephone communications with Phnom Penh appeared to have been cut. Radio and television stations continuously played a taped speech by the apparent coup leader, Send Prime Minister Hun Sen.

Rival forces of Hun Sen and First Prime Minister Prince Norodom Ranariddh opened fire with rockets, artillery and small arms as soon as dawn ended an all-night curfew.

Shortly before 8 a.m., a vast plume of black smoke was seen rising over the northwestern part of the city. A fuel storage dump was believed to have been hit, but that could not be immediately confirmed.

In a statement faxed Sunday to news organizations in Phnom Penh, Ranarridh accused his longtime rival of attempting an illegal power grab, and declared he was now the sole rightful ruler of Cambodia.

``Mr. Hun Sen has now placed himself outside the law,'' Ranariddh said. ``The only government is the one over which I preside.''

Ranariddh has not been seen since he reportedly left Cambodia for France on Friday, however, and the fax gave no clue as to his whereabouts.

Hun Sen and Ranariddh formed a shaky coalition government in 1993 after spending years as enemies on Cambodia's battlefields in the country's long civil war.

Weeks of rising tensions and isolated clashes erupted into a bloody mortar and rocket battle in the capital Saturday when Hun Sen's forces launched an offensive against troops loyal to Ranariddh.

Dozens of rocket and mortar rounds slammed into several areas of Phnom Penh, killing at least four people and wounding 29, hospital and military officials said. A 4-year-boy hit by shrapnel was among the wounded.

The battle in the city came hours after troops loyal to Hun Sen wrested control of a military base near the airport from forces aligned to Ranariddh. Hun Sen's troops also surrounded a second base near the airport on the outskirts of Phnom Penh.

On Sunday, Ranariddh's top military commander, Nhek Bunchhay, was holed up in the base.

``We're in our trenches, everything's OK,'' he told The Associated Press. ``They can't take us.''

Wearing camouflage fatigues instead of his usual civilian suit, Hun Sen appeared on national television Saturday to accuse Ranariddh of treachery and of preparing for civil war.

``Prince Norodom Ranariddh and a number of accomplices have illegally imported weapons in an ill intention to provoke a war,'' Hun Sen said, in remarks broadcast repeatedly Sunday.

Reports Sunday suggested that Hun Sen may now be visiting neighboring Vietnam, whose leaders have been his allies. There was no independent confirmation.

Roads leading into Phnom Penh from the west were sealed by Hun Sen's troops. The airport was closed by the end of the day.

Hun Sen's moves had all the trappings of a military coup, but his defense minister denied there was a plan to oust the prince.

``This is not at all any coup d'etat,'' said Tea Banh, a co-defense minister who backs Hun Sen's Cambodian People's Party. His counterpart from Ranariddh's royalist party also was out of the country.

Foreign diplomats warned Tea Banh against increasing the violence.

``Our citizens are all here to help Cambodia,'' U.S. Ambassador Kenneth Quinn told The Associated Press. ``They can't afford to be in danger and it won't be understood if there is fighting and foreign citizens are put at risk.''

Hun Sen's troops said the two bases at the center of Saturday's fighting were used by Ranariddh's political party to house defecting Khmer Rouge rebels.

The Khmer Rouge, which ruled the country from 1975-79, has been neutralized by defections, attrition and a split that led to leader Pol Pot's reported capture last month by his own troops. Both premiers have been trying to recruit the disaffected rebels to strengthen their own hands, and the issue deepened tensions between the two leaders.

Hun Sen, a former communist who ruled Cambodia through the 1980s with Vietnam's backing, has accused Ranariddh of trying to resurrect the Khmer Rouge.