Mexican police are investigating online adverts posted by apparent hitmen offering to carry out killings for as little as $6,000 (£3,000) per person.
The classified ads have appeared alongside notices posted by people selling home appliances or renting accommodation, police in Mexico City say.
In one, an "ex-military hitman" who describes himself as "professional and discreet", promises a "job guaranteed in 10 days or less", adding: "I have worked in Spain, only serious offers, 6,000 dollars."
Another, entitled "Hitman - Killer for Hire", reads: "Problems with a certain person? Want it taken care of? Write me. I am 100 per cent professional and don't charge in advance."
Although the adverts have not been verified, Mexican officials said they were taking them seriously against a backdrop of increasingly brazen tit-for-tat murders by rival drugs cartels and organised gangs.
Gangs are known to turn to professional assassins using high-calibre weapons for targeted killings, which have recently become more public with evidence of slayings such as bodies and severed heads left in streets.
Since the government declared its offensive against organised crime in December 2006, there have been more than 3,500 drug-related killings, according to estimates, with anywhere from 1,000 to 1,700 this year. The dead include gang members as well as hundreds of police officers and public officials.
In one of the latest incidents last week, a senior police official who helped spearhead the drive against organised crime was shot dead at close range by a gunman thought to be working for a cartel.
"The problem of hitmen is real and we are facing it all over the country - people offer their services to kill someone for a price," police official Miguel Amelio Gomez told the daily Reforma newspaper.
Earlier this year Mexican drug gangs issued a call via Guatemalan radio for ex-elite soldiers to work as smugglers. Meanwhile, an armed wing of one trafficking organisation, the Gulf cartel, placed banners in US/Mexico border towns advertising for new recruits.
Mexico's slow and ineffective justice system means deaths are often not investigated and killers remain at large.
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