BOGOTA (Reuters) - Reduced groups of protesters are expected to gather in the Colombian capital Bogota on Thursday to mark an eighth day of anti-government protests in the Andean country, as a major union called for an additional strike on Dec. 4.

The number of protesters has gradually fallen from a 250,000-person march and initial strike last week.

Demonstrators are rallying against economic plans - such as a rise in the pension age and a cut to the minimum wage for young people - that President Ivan Duque denies supporting, as well what they say is a lack of government action to stop corruption and the murder of hundreds of human rights activists.

The injury and eventual death of 18-year-old protester Dilan Cruz has also motivated demonstrators, who are calling for the ESMAD riot police to be dissolved.

The visibility of the ESMAD force during protests has been significantly reduced since Cruz was injured on Saturday.

The country's forensic medicine department confirmed on Thursday that Cruz had been killed by a projectile launched by the ESMAD.

Protests attracted thousands of demonstrators to several places around Bogota and in other cities on Wednesday, with the ESMAD making a late night appearance to disperse a crowd in the north of the city.

The head of the Central Union of Workers (CUT), part of the group of unions and student organization which called the original strike, urged people to join a strike next week.

"We are going to focus all our efforts so it is felt in the whole country," CUT president Diogenes Orjuela told a local TV channel late on Wednesday.

The protests have caused problems for Duque's proposed tax reform, with opposition parties leveraging demonstrations in a bid to force the government to make significant changes.

"The strategy of the government seems to be to hang in there until Dec. 8, when Christmas season starts," said analyst Sergio Guzman of Colombia Risk Analysis. "The marches have now lost their greatest asset - the diversity of protesters."

But the new year may bring new challenges for the embattled Duque, Guzman said.

"The deeper problems remain and the protests could be revived next year."

Protests, which were marked by isolated looting and curfews on Thursday and Friday, have caused widespread transport problems in Bogota, with commuters forced to walk for hours to reach their homes as demonstrators blocked roads.

Marches are planned along at least two routes in Bogota on Thursday afternoon.

(Reporting by Julia Symmes Cobb; Editing by Marguerita Choy)