At each roadblock there are a dozen or so of these boys, grenades casually hanging from their fingertips or in their belts. Mostly they are accompanied by soldiers armed with automatic weapons. By midday, after downing banana beer, their temper has become unpredictable. They lean through the car window, peering into your eyes and fingering your identity papers which they cannot in any case read. 'Pas d'argent? No money? Give me a beer]'
It is impossible to forget that to them killing is as casual an act as brushing off a fly. Our hope was that they would respect the authority of our army escort. But the soldiers appointed to accompany our vehicle by the defence minister - now holed up with the rest of the Rwandan cabinet at a civil service training centre in the grubby little town of Gitarama, 25 miles south of the capital - were as frightened as we were. The proximity of the Rwandan Patriotic Front (RPF), which last month surged southwards into the outskirts of the capital, did little to relieve their anxiety.
As we neared Kigali the road became thronged with ragged civilians fleeing ahead of the rebel advance. Whimpering children followed their over-burdened mothers. Artillery sounded ahead of us.
The final approach to the city is heralded by barriers of trees and rocks placed at 100-yard intervals along the road. Apart from the militias and soldiers, scarcely a soul is to be seen on the streets.
Kigali comprises a series of hillside settlements around a small town centre containing the market, shops, hotels and offices. Until recently 350,000 people lived here. Now it is a ghost town. At least 60,000 inhabitants, largely Tutsis and suspected rebel sympathisers, were last month massacred mostly by the Hutu Interahamwe.
I remembered Kigali last summer. The peace accord which would bring to an end nearly three years of civil war was shortly to be signed and the mood was one of optimism.
Although more than a million people had been driven from their homes by the war and the economy was in ruins, everyone was looking towards a peaceful future.
I interviewed the late president, Juvenal Habyarimana, who expressed concern about his fellow politicians' slim grasp of democracy. But he was resigned to admitting the RPF into an enlarged transitional coalition alongside those opposition parties which, since the end of single-party rule in 1992, had joined his MRND party in parliament. Those days of calm were shortlived. All opposition members have either fled or been killed. The Tutsi-dominated RPF has relaunched its war against a government which now comprises only hardline representatives of the Hutu majority. Hundreds of thousands of Tutsis are believed to have been massacred by the death squads.
Deafening bangs of outgoing mortar rounds resounded against the rumbles of shelling in the outskirts as we entered the centre of Kigali. We passed the Eglise de la Sainte Samille, where earlier this month 13 people were killed and more than 100 injured when an artillery shell hit the compound. An estimated 8,000 displaced people are camped around the church. Nearly 400 terrified Tutsis have taken refuge in the Hotel des Milles Collines whose entrance is guarded by armed Interahamwe. This is one of the few locations where UN monitors are protecting civilians.
Half of Rwanda, including the north and east, is under rebel control. In the south-east the RPF has pushed as far as the Burundi border. Though there is no indication that Kigali is likely to fall to the rebels in the next few days, shelling of the city is intense. On bad days, civilian casualties can be counted in their hundreds. The RPF controls several strategic hillside positions, though the centre, airport and army barracks remain in government hands.
As we arrived at the Central Hospital, three badly wounded men were being removed from the back of a transit van. One casualty was manhandled on to a blood-stained stretcher while another was levered out on a foam mattress, his face and legs shattered by shrapnel wounds. 'There are over 3,000 injured and sick here,' the hospital director, Dr Faustin Kanyangabo, said. 'We have terrible hygiene problems - no running water, hardly any medicines or dressings. The wounds are appalling and we're having difficulty coping.'
The floors of the wards are filled with wounded men, women and children. They have been operated upon and patched up as well as is possible but with only six doctors the situation is clearly desperate.
At the top of the International Committee of the Red Cross compound, overlooking the eastern reaches of the city, is an airy green tent containing 15 wounded orphans. One little girl of eight, who had been repeatedly raped by militiamen, lay motionless on a mattress beside another child whose bandaged stump of a leg protruded from underneath a blanket.
As the shelling intensified our army escort became increasingly agitated and we were ordered to leave the city. The rebels, already in control of the northern and eastern approaches to Kigali, are circling to cut off the vital road southwards to Gitarama where the interim government ponders its fate.