Two police chiefs have been killed in Mexico, in what authorities believe is an escalation of drug-related violence along the US border.
More than 100 people were killed last year along the border
The chiefs were shot by unknown gunmen in separate attacks in Nuevo Leon state, bordering Texas, police said.
Rival drug cartels in Mexico have been battling for control of drug-smuggling routes to the US.
More than 100 people were killed in related violence last year - including about a dozen police personnel.
In the first of the two attacks, armed men burst into a police station in the town of Sabinas Hidalgo and snatched chief Javier Garcia at gunpoint.
His body was later found handcuffed with a gunshot wound to the back of the head, authorities said.
Hours later, gunmen killed Hector Ayala, the police chief of San Pedro Garza - a wealthy enclave of state capital Monterrey - as he was driving through the city.
Most of the violence had previously been limited to Nuevo Laredo, a city on the Texas border in neighbouring Tamaulipas state.
Last week, a Mexican journalist was seriously injured there after gunmen stormed the offices of a local newspaper.
Meanwhile, Mexico's President Vicente Fox has announced that his government will start extraditing major drug traffickers to the United States soon.
He said it would be a way to stop cartel leaders operating on Mexican territory.
His comments follow two court rulings which established that Mexico could extradite drug traffickers provided they did not face execution in the US.