WASHINGTON (Reuters) - The U.S. Agriculture Department is testing some chicken flocks on American farms as well as migratory birds in Alaska to detect any sign of the deadly bird flu disease, federal officials said on Wednesday. 

The H5N1 strain of avian influenza, which can be lethal to humans, was found in poultry in Asia before moving into Romania, Turkey, Greece and Russia in recent weeks. No cases have been found in the United States. 

"For more than two decades, USDA has worked to prepare for and prevent an outbreak of dangerous strains of avian influenza in our country," Deputy Agriculture Secretary Chuck Conner said in a statement. 

"We also have strict importation restrictions to prevent the spread of the virus in our country and an elaborate surveillance system in place to monitor our bird populations." 

Conner and other USDA officials held a technical briefing on Wednesday to discuss the federal government's surveillance system. 

To help detect the highly transmissible form of bird flu, the USDA said it has more than 40,000 private veterinarians across the nation watching for the disease. 

The USDA is also working with the U.S. chicken and turkey industries to randomly test commercial flocks and poultry showing signs of illness. 

USDA scientists have also been testing wild migratory birds since 1998 in the Alaska flyway, it said. 

The USDA also maintains a supply of bird flu vaccine for poultry that could be used to create a buffer zone if the disease is ever found in the United States, it said. 

Last year, five U.S. states had an outbreak of a mild strain of bird flu. 

The United States is the world's largest exporter of broilers, and is expected to ship some $1.8 billion worth of chickens in fiscal 2005. 

According to the U.S. Centers for Disease Control and Prevention, there is no evidence of any human cases of bird flu from eating poultry products. Cooked poultry products pose no risk to human health.