The rebel-led ousting of the Yemeni government has left the Pentagon in the dark and unable to monitor the hundreds of millions of dollars worth of weapons provided to the country over the years.
Houthi rebels took over the capital of Sana last month and prompted the resignation of President Abd Rabbo Mansour Hadi.
The official Houthi slogan and emblem says, "Death to America, death to Israel, damnation to the Jews," notes The Independent.
Now those rebels are said to have full control over the military's weapon depots and bases, which contain U.S.-provided heavy weaponry, including tanks and artillery, the Guardian reported.
The unrest has limited the U.S. military's "ability to conduct routine end-use monitoring checks and inspections we would normally perform," a U.S. official told the Guardian, though the official would not specify which equipment it lost track of.
The U.S. has provided more than $400 million in weapons to Yemen since 2006, according to congressional research estimates, including helicopters, night-vision and surveillance technology, military radios and transport aircraft.
"We continue to monitor the situation in Yemen closely and, as the security environment permits, we will continue working with the Government of Yemen to ensure equipment granted or sold to the Government of Yemen by the United States remains accounted for," the official told the Guardian.
Al-Qaeda also has a large presence in the country, and has vowed to fight the Shia Houthi rebels to defend the Sunni population, according to The Independent.
It's still unclear who Yemen's military remains allegiant to and the integrity of the chain of command is also questionable, but the Pentagon has indicated it's willing to engage the Houthis.
Pentagon spokesman John Kirby said last week that it is "accurate to say that the Houthis, as participants in these events, will certainly have reason to want to speak to international partners and the international community about their intentions."
"Given the political uncertainty, it's fair to say that US government officials are in communication with various parties in Yemen about what is a very fluid and complex political situation."
Last month, President Barack Obama said that rather than send troops to Yemen, the most sustainable option is to continue with the drone program.
"It is not neat and it is not simple," Obama said. "But it is the best option that we have."