BOGOTA, Colombia (Reuters) -- A provincial mayor was shot dead on
                  Tuesday and 19 government investigators were kidnapped as gunmen of the
                  left and right intensified a campaign of violence across Colombia.

                  The attacks came two days after Marxist rebels bombed the country's
                  largest oil pipeline in northwest Antioquia province and a fireball of blazing
                  crude destroyed two nearby villages.

                  Health authorities said Tuesday the death toll from that attack by the
                  National Liberation Army (ELN) had risen to 50 as more of the injured died
                  in hospital.

                  In Tuesday's violence, a suspected right-wing death squad murdered mayor
                  Hector Piedrahita near the northwest town of Anori, police said. He was the
                  11th Colombian mayor to be killed this year.

                  He was apparently pulled from his car along with his driver and a human
                  rights official, who were also killed, on the outskirts of Anori. Their
                  bullet-riddled bodies were dumped on the roadside and the car was found
                  abandoned.

                  The murdered mayor had been kidnapped in August along with seven other
                  mayors from the same province by the National Liberation Army (ELN), the
                  country's second-largest Marxist guerrilla group, and held for six weeks
                  before being released.

                  In a separate incident in the Sierra Nevada de Santa Marta mountain range,
                  in northern Colombia, unidentified gunmen kidnapped 19 investigators from
                  the Chief Prosecutor's Department.

                  The officials had been on their way to investigate last week's massacre of at
                  least 17 peasants by an ultra-right paramilitary gang.

                  Authorities said the investigators had been ambushed but declined to say
                  who may have been responsible for the attack.

                  Local media, however, blamed ELN guerrillas who are known to operate in
                  the region.

                  This week's attacks offered little hope of any immediate let-up in Colombia's
                  long-running civil conflict even though the government, right-wing
                  paramilitary groups and the main guerrilla groups have all pledged to take
                  part in peace talks.

                  At least 35,000 people, many of them civilians, have died as a result of the
                  war in the last decade alone.

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