BEIRUT, Lebanon (AP) – Shellfire hit Beirut’s airport Sunday, and radio reports said the home of the U.S. ambassador was struck during fierce duels between Syrian gunners and Christian army units. Police reported 13 people were killed.

Thunderous explosions rocked Beirut in what authorities called the heaviest artillery duel since the 14-year-old civil war renewed fighting March 8.

Syrian and allied Druse gunners poured more than 8,000 rounds, at a rate of up to 100 per minute, on east Beirut and the Christian suburbs northeast of the city in 24 hours, a police spokesman said.

Christian soldiers of army commander Gen. Michel Aoun struck back with 155mm howitzers, firing at least 3,000 rounds on Syrian positions in Moslem west Beirut, the central mountains and east Lebanon’s Bekaa valley, the spokesman said.

He said Christian gunners also blasted the Beirut-Damascus highway in the mountainous Dahr al-Baidar region in an apparent bid to block the way of Syrian tanks poised to roll into Beirut.

The spokesman, who cannot be named under standing rules, said eight people were killed and 20 wounded in the Christian side and five killed and seven wounded in Moslem west Beirut.

The confrontation has exacerbated a political crisis that created competing Christian and Moslem governments and split the army on sectarian lines.

“Have mercy on the helpless people,” pleaded Acting Prime Minister Salim Hoss, who heads a mostly Moslem Cabinet vying for legitimacy with Aoun’s Christian Cabinet.

“I appeal to all those pulling gun triggers to stop shooting at once, stop this bloodbath, stop this massacre,” he said in an appeal broadcast by Moslem radio stations.

Aoun has declared a “war of liberation” against Syria, which has 40,000 troops in Lebanon and has become the country’s main power broker during the civil war.