Gunmen seriously wounded the mayor of a Manila suburb and killed seven of his bodyguards today in the bloodiest attack in the capital blamed on communist rebels. Gunmen also shot dead a businessman. Police said Mayor Prospero Oreta of suburban Malabon suffered three gunshot wounds in the mouth, chest and arm but was out of danger after surgery. Seven of his bodyguards died in the attack and another was in serious condition. The ambush occurred as military units in various parts of the country were on full alert in anticipation of stepped up rebel attacks marking Tuesday's 19th founding anniversary of the now 24,000-member communist New People's Army. Seven hours after the ambush, three men in a car shot a businessman while he was driving in suburban Quezon City, just north of Manila, police said. The victim, who died at a hospital, was identified as Francisco Castro. Police said they had no idea who his attackers were or what their motive was. But the victim's brother, Jose Castro, vice president of the Manila chapter of the leftist People's Party, told reporters he believed he was the real target. Radio and newspaper reports said police Manila had received a call from the Alex Boncayao Brigade, the communist guerrilla unit operating in the Manila area, claiming responsibility for the ambush on Oreta. Police declined to confirm the reports. Armed forces spokesman Col. Oscar Florendo confirmed such a call had been received, but added the army could not yet say if the guerrilla unit was behind the attack. The Alex Boncayao Brigade has been blamed for the killings of more than 150 policemen and soldiers in daylight ambushes on Manila's streets since last year. Before today, the attacks have killed one or two people. The rebels had announced they would soon kill officials as well as police and soldiers. President Corazon Aquino said she was ``shocked and saddened by these acts of violence.'' ``I have always asked our people to resort to the ways of peace,'' she said in a statement. ``My hope is that as democracy in our country gains a strong foothold, violence and terror will gradually rescind.'' Investigators said Oreta and his party were riding in a van and a car to a flag-raising ceremony at the Malabon town hall when six men waiting at an intersection opened fire with automatic weapons. Cpl. Mario Odulio said the killers were armed with AK-47 and M-16 automatic assault rifles as well as 9-mm and .45-caliber pistols. Police recovered more than 40 spent shells at the scene, Odulio said. He said the killers escaped aboard a van and a jeep. Police said they believed the killers belonged to the Sparrow Unit, an assassination squad of the New People's Army, but were also looking into the possibility local politics was involved. Malabon, a fishing community in Manila's northern suburbs, was among the places where last January's local elections were hotly contested. Oreta is a brother-in-law of Rep. Tessie Oreta, younger sister of Mrs. Aquino's assassinated husband, former Sen. Benigno S. Aquino Jr.