A new report issued by a panel of retired U.S. generals and admirals is warning that America's dependence on fossil fuels is a grave threat to the nation's security.

In the report the retired military leaders, who make up a group called the Military Advisory Board, say America needs to immediately begin moving away from reliance on fossil fuels and diversify its energy sources.

The board's chairman is retired Air Force General Charles Wald.

"We found that America's current energy posture constitutes a serious and urgent threat to our national security.  This is a threat that can and will be exploited by those who wish to do us harm," he said.

Wald is one of a dozen former high-ranking military officers who unveiled the report during a news conference in Washington.

The retired general says America's dependence on fossil fuels is undermining the nation's economy and leaves the country vulnerable to unstable or hostile regimes.

"The energy threat impacts our foreign policy.  Our dependence on oil, not just foreign oil, reduces our leverage internationally and sometimes limits our options.  I say all oil because we simply do not have enough resources in this country to free us from the stranglehold of those who do.  We find ourselves entangled with unfriendly rulers and undemocratic nations simply because we need their oil."

The report says inefficient use of and over reliance on oil burdens the U.S. military, reduces combat effectiveness and exacts a huge price tag in dollars and lives.

Defense Department officials say the Pentagon is the largest consumer of energy in the United States and last year spent 20 billion dollars on petroleum products.

Officials say 70 percent of the U.S. military convoys in Afghanistan are carrying fuel and water.

The report says enormous resources are used to protect such convoys as well as shipping lanes around the oil-rich countries in the Persian Gulf.

General Wald says another major concern is the nation's aging power transmission network.

"We found that the fragile state of America's domestic electricity grid is, in fact, a serious threat to our national security.  Nearly all of our stateside military installations depend on our domestic electricity grid.  When it fails, critical elements of our military and homeland security systems can also fail and impact missions overseas," Wald said.

The retired military officers called on the Defense Department to take a leadership role in transforming America's energy policies.

They say the Pentagon can stimulate the market for new energy technologies and vehicle efficiencies.

Retired Vice Admiral Dennis McGinn says a reduction in the use of fossil fuels can slow global warming, which the retired military officers say is also a threat to national security.

"Global climate change will pose serious threats to water supplies and agricultural production.  At the same time we will see increasing demand for the dwindling supply of fossil fuel.  These factors mean an intense competition for key resources and that leads to conflict," McGinn said, noting that the U.S. must prepare for such conflicts.

The retired military officers say the destabilizing nature of scarce resources and climate change are likely to increasingly drive U.S. military missions for the rest of this century.