Was this the first casualty of Lebanon's new civil war?

A poster of Ahmed Ali Mahoud looked down on the wailing crowd who had gathered to mourn his death. Written underneath the photo of Ahmed, 21, were the words "a martyr for national unity". But many of the people who gathered outside the Husseiniyah, the traditional Shia building of mourning, were fearful of the implications of his death - that Ahmed Mahmoud might have been the first victim of the next Lebanese civil war.

Receiving condolences from the large crowd was Ahmed's brother-in-law Haitham. A tall, quietly spoken man, Haitham, 34, said he believed Ahmed was murdered by Sunni Muslims who were out to kill Shia. "They see we are many and very strong," he says. "And they are very few, those of Saad Hariri's [Sunni] movement."

"We stood against Israel and we will stand against the ones in charge now," screamed an old veiled woman outside the mourning room. "If Saad Hariri wants to make it a sectarian issue, let him come here to Dahieh and we will show him our men".

Inside, the women were sobbing while the men sat quietly with their heads in their hands. "Where is Ahmed, where is Ahmed?" shouted Ahmed's girlfriend, Ishan, 20, as she threw herself to the ground. The young couple were to be engaged this week.

A supporter of the Hizbollah-allied Amal movement, Ahmed and his teenage brother Hassan were returning home late on Sunday night from the large anti-government rally when they walked into a confrontation between Sunni and Shia youths. "We saw people coming down towards us throwing stones," said Hassan. "So we started to run away - but while we were running, the shooting started and that's when my brother was shot in the back."

Hassan did not see who fired the shots, but he said he believed it was young men from the Sunni Future Movement, led by the murdered ex-prime minister Rafik Hariri's son Saad, who shot at them. "It was the Future Youth," said Hassan. "The shots came from their direction."

The second eldest of eight brothers and sisters, Ahmed had finished his compulsory military service and had spent the past two years working in the local mechanic's shop. "They killed a child, just look at his picture," said Ahmed's boss Mazen. "He never hurt anyone."

Ahmed's was one of the very few Shia families in the predominantly Sunni neighbourhood of Tareeq Aljadida. All over the neighbourhood are pictures of the murdered former Sunni prime minister Rafik Hariri and his son. "God be with you, Saad Hariri!" shouts a young man riding past on a motorbike.

Amid the mourning scenes yesterday came the announcement that Ahmed's funeral had been postponed for 24 hours as rumours circulated that another Shia youth had been killed in sectarian violence. Security remains tight in downtown Beirut, where thousands of anti-government supporters are camped out for their fourth day of protests.

But the man whose resignation they are demanding is refusing to make any compromises. Bolstered by Western and Arab support, the Lebanese Prime Minister Fouad Siniora has insisted that his government will not be affected by the protests.

Following a meeting with the embattled Mr Siniora, the Arab League Secretary general Amr Moussa said that "national consensus is the basis for any Arab action, we are working for Lebanon and must work things out on the basis of national unity." Mr Moussa also held midnight talks with representatives of the Hizbollah leader Hassan Nasrallah.

In southern Lebanon, the Israelis agreed to withdraw their soldiers from the last part of the village of Ghagar, a Druze hamlet, and allow UN troops to take control. But their overflights continued above Lebanon, despite French protests, and Israel still claims Hizbollah is importing arms from Syria in contravention of UN Security Council resolutions.

The UN has stated that it is not mandated to search for guerrilla weapons in southern Lebanon.