Last month, the United States Embassy in Kuala Lumpur sent a warning to American citizens here: “Remember to carry your backpack or purse on the shoulder AWAY from the road to prevent having it snatched by motorbikers.”

The possible reasons for a higher crime rate are a matter of debate — some say the country’s ethnic-based policies that favor majority Malays are partly to blame; others say the police force is corrupt and ineffectual. Even the extent of the crime wave in this country of 29 million people is in question.

Despite the widely held perception of a sustained crime wave, the government says that after doubling from 2000 to 2009, the number of reported cases of violent crime nationwide has declined sharply since then. Government officials say they have achieved the drop by adding police officers on the streets and security cameras and barriers along roads to deter thefts by people on motorbikes, as well as by studying policing methods in cities like New York.

But a series of high-profile crimes this year — including some against government officials or their relatives — have led the authorities to begin to acknowledge the depth of the problem. Since August, the police have arrested more than 11,000 people suspected of being gang members. And in a reversal of earlier changes meant to shed some of the country’s authoritarian legacy, the government last month passed laws that would give the police the authority to detain suspects without trial.

As worries rise, the opposition says the government is manipulating the statistics. Critics note that, after years of providing the public with data on murders, rapes, thefts and other crimes, the government has changed the way it presents crime statistics, focusing on what it calls “index crimes” rather than giving a detailed accounting. Tony Pua, an opposition member of Parliament, said he had “no confidence at all” that the figures were accurate.