Four policemen have been killed after attackers ambushed their vehicles in Mexico's western Michoacan state.
Another four policemen were injured in the attack, which happened after officers were sent to a ranch to rescue a kidnap victim, local authorities said on Tuesday.
The suspected kidnappers fled the scene after Mexican army reinforcements arrived, abandoning 16 high-calibre rifles, 48 chargers, eight guns and five grenades.
The kidnap victim was reportedly rescued alive after the incident.
Mexico is battling an increasingly bloody war with drug cartels which are also fighting each other for lucrative trade routes into the US.
Meanwhile in Mexico's north, five more people were reported killed in three separate incidents.
Two of the victims were shot dead in the border city of Ciudad Juarez while two more were killed in Chihuahua capital and one died in Coahuila state, the state prosecutor's office said on Tuesday.
Obama plan
Also on Tuesday, two US senators on Tuesday proposed spending $550 million more to address security problems along the border with Mexico.
Joe Lieberman, senator for Connecticut and Susan Collins, senator for Maine, proposed adding the funding to the senate's 2010 budget plan in a bid to halt the trade of drugs from Mexico and to stem the flow of guns south from the US.
Last week Hillary Clinton, the US secretary of state, admitted during a visit to Mexico that "insatiable" US demand for drugs was driving the surge in gang violence near the border.
Barack Obama, the US president, has unveiled a $184m plan to step up searches for smuggled drugs, guns and cash at the Mexican border.
More than 1,000 people have been killed so far this year in drug-related violence in Mexico.
Felipe Calderon, the Mexican president, declared war against the country's drug gangs shortly after taking office in 2006, sending thousands of troops to the border, a move which sparked an explosion of violence from the cartels.
Calderon is due to hold talks with Obama on April 16 and 17 in Mexico.