By Laura Zuckerman

Feb 13 (Reuters) - The number of imperiled wolves found only in the American Southwest climbed to 109 in 2014, marking the fourth consecutive year that the population of Mexican gray wolves has risen by at least 10 percent, federal wildlife managers said Friday.

Wild Mexican wolves were believed to be all but extinct in the United States in 1998 when the U.S. Fish and Wildlife Service began reintroducing the animal to its native range.

At that point there had been no sightings of the wolves, which are native to western Mexico's Sierra Madre mountains, in the wild in the United States since the 1970s, said Benjamin Tuggle, the Service's southwest regional director.

Government and tribal biologists seeking to restore the creature to Arizona and New Mexico estimated in 1982 that the recovery number needed for the survival of Mexican wolves - a smaller, separate subspecies of the gray wolf found elsewhere in the United States - was no fewer than 100 animals.

"Although there is still much to be done, reaching this milestone is monumental," Tuggle said in a statement about the 2014 annual survey showing a minimum of 109 Mexican wolves, up from 83 at the end of the previous year and more than double the population found in the two states in 2010.

Tuggle said the federal, state and tribal team overseeing recovery of the Mexican wolf began using a technique last spring known as cross-fostering which involves placing "genetically valuable" pups into similarly aged litters of established packs in a bid to improve the genetics of the wolves.

He said new methodology, combined with population growth, bode well for the future of the rare animal.

The Fish and Wildlife Service said last month that Mexican wolves will be allowed more room to roam in the U.S. Southwest, but could be marked for death if they preyed too heavily on elk and deer prized by hunters.

The Mexican wolf, considered one of the most imperiled mammals in North America, has been at the center of a conflict that has pitted ranchers and hunters against conservationists who are petitioning the government for more measures to ensure the animal makes a strong comeback.

In Mexico, the animals are believed to have been extinct in the wild since the 1980s. In 2014, wildlife managers there announced the first litter of wolf pups to be born in the wild since then, local media said, following reintroduction programs. (Reporting by Laura Zuckerman in Salmon, Idaho; Editing by Daniel Wallis and Sandra Maler)