MEXICO CITY—The Mexican drug war has claimed more than 51,000 lives in the past five years, and while initial signs point to the conflict stabilizing in some of the bloodiest areas, particularly along the Texas border, the violence is increasingly spreading into the country’s interior, according to analysts and government officials.

Signs also point to further fragmentation among the cartels, although the paramilitary group known as the Zetas, with links to Dallas, has strengthened and is now considered the fastest-growing criminal group and the most powerful force threatening the country’s national security.

“After a dramatic increase in previous years, violence levels seem to be slowly stabilizing,” said Eduardo Guerrero Gutierrez, a security analyst at Lantia Consultores, a Mexico City consulting firm.

He said his figures showed more than 16,600 people killed in 2011. Guerrero’s figures have been closely aligned with the federal government’s statistics.

“In some cities, there has even been a sustained improvement in violence levels. Nevertheless, geographical dispersion of violence continues,” Guerrero added, quoting his own study to be published this month in one of Mexico’s leading intellectual magazines, Nexos.

In 2011, homicides rose by 11 percent, a far slower rate than in previous years. Political parties have staked out violence as the key issue in presidential elections this July.

Although violence has leveled off, the northern states of Chihuahua, Coahuila, Nuevo Leon and Tamaulipas—all bordering Texas—remain among the bloodiest in Mexico. Last month, the military announced that it will beef up forces in the region.

“In spite of a number of arrests and hits, the Zetas continue to defy both governments,” said a US intelligence official on the border, speaking on condition of anonymity. “It’s speaks to both their resilience and skills of recruiting young, often desperate people who want to ‘make it’ quick and easy.”

New killings have shattered a relative peace in Ciudad Juarez, where more than 13 law-enforcement officials, mostly local police, have been gunned down in recent days. A group calling itself the New Juarez Cartel has vowed to kill a police officer each day until Police Chief Julian Leyzaola either stops pursuing the group or leaves the city altogether.

The chief has reacted by sending police to stay in hotels, since most of the killings have happened as they leave or return home.

A recent study released by the Citizens’ Council for Public Security and Justice, a Mexican research group, listed five Mexican cities as among the world’s most violent: Ciudad Juarez, Acapulco, Monterrey, Torreon and Chihuahua. All but Acapulco are in states bordering Texas.

Meanwhile, violence levels have risen to the south, in the states of Veracruz, Jalisco and Guerrero and even in Mexico City, which has occasionally seen flare-ups, though the violence hasn’t been as sustained as in other states.

Vanda Felbab-Brown, an expert at the Washington-based Brookings Institution, said the decline in killings in some areas may be more the result of one cartel exerting overall control rather than specific success by the military or federal police.

“The violence is leveling off some, but this is not because the policy is effective, but because the tempo of violence has been extraordinarily high, very costly and very difficult to maintain,” she said.

“Mexico has lost as many people in five years as the number of Americans killed during the Vietnam War over a 25-year stretch. Life and death in Mexico is so cheap and systematic. These are not disconnected murders but linked to competition over formal and informal parts of the economy in Mexico.”

The latest casualty figures do not include the estimated 10,000 people who have disappeared since President Felipe Calderon launched the crackdown in late 2006. Some analysts and experts put the loss of life at 60,000 or higher.

Calderon remains defiant in his decision to tackle the cartels, even as opposition grows on the part of political rivals and nongovernmental organizations. They question not so much the reason for going after cartels, whose power had long been established, but whether his administration was adequately prepared to face an enemy that has penetrated the very fabric of society and public institutions.

Calderon recently reiterated that his strategy is based on weakening cartels, capturing top leaders, confiscating their assets and strengthening judicial institutions. The key, he said, is to strengthen the social fabric through a more vibrant civil society, a process similar to “planting a tree for a better Mexico, a more secure, more prosperous and more just country.”

Confronting criminals, he added, is like “taking out the bad weed that finishes off the nutrients and finishes off the plants.”

Critics, however, question how the government can claim that most of the victims are criminals when victims are often not identified. An estimated 95 percent of all crimes are never solved.

“The administration has focused on capturing, killing, extraditing people and has argued that the violence is a regrettable but necessary piece to that strategy,” said Eric Olson, a Mexico expert at the nonpartisan Woodrow Wilson International Center for Scholars in Washington, D.C. “But if you lost a daughter, son, brother or sister, it’s not a satisfying argument. It’s hard to convince the Mexican public that this is success.”

Even in cities such as Ciudad Juarez, where overall crime dropped by 40 percent in 2011, residents remain skeptical.

Nightclub owners tout a renaissance of nightlife, signs that Juarenses are slowly taking back their city.

But Octavio Mares, a cab driver, isn’t so sure. The city recorded about 120 killings in the first month of 2012.

“I want to believe the news, just I like I want to believe in miracles,” he said. “Only time will tell.”