Lawmakers are stepping up their scrutiny of the United States' access to rare earth minerals that are used to make clean energy products like hybrid cars, wind turbines and energy efficient lighting.

Recent developments in China -- where 97 percent of the world's rare earth metals are produced -- have triggered comments by lawmakers and placed additional importance on hearings already scheduled on this issue. The New York Times reported last week that Chinese officials were blocking shipments of rare earth metals from China to Japan.

"What it points out is that we need to restart our own rare earth mineral mining," Sen. Mark Udall, D-Colo., said last week of the news.

A subcommittee of the Senate Energy and Natural Resources panel will hold a hearing on this topic Thursday; it was scheduled before the news from China developed, but it should get more attention given the development. "I think it adds a sense of urgency to the hearing," Udall said. "It of course has been under the radar screen -- that is, the need for rare earth minerals -- but I think now a lot more people know the importance of them."

The hearing Thursday will include testimony from David Sandalow, the Energy Department's assistant secretary for policy and international affairs. It will also examine legislation introduced by Senate Energy and Natural Resources ranking member Lisa Murkowski that authorizes the Energy Department to issue loan guarantees to rare earth minerals projects and includes other measures aimed at jumpstarting domestic rare earth minerals production, which is at a standstill. Murkowski's measure resembles a bill a House committee approved last week and is scheduled to be voted on by the full chamber later this week.

The United States has one major known mine that holds rare earth metals, but it is not open for mining. "There is a site in California that has been mothballed," Udall said. "We ought to accelerate the reopening of that site so we can produce our own rare earth metals." A company based in Udall's state -- called Molycorp -- owns the California mine, and it has taken the initial steps to reopen it.

House Global Warming Chairman Edward Markey sent a letter Monday to several top administration officials seeking answers regarding both the specific news regarding China blocking shipments of rare earth minerals but also more general inquiries about how the United States can become more independent in their production. "The recent events with Japan aside, the trend in Chinese rare earth trade policies are disturbing and bring into great doubt China's claim that it is a reliable global supplier of rare earth elements," Markey said in the letter, which was sent to Energy Secretary Chu, Defense Secretary Gates, Commerce Secretary Locke and U.S. Trade Representative Kirk.