U.S. airlines have voluntarily agreed not to fly in the airspace near the Ukraine-Russia border, the U.S. Federal Aviation Administration confirmed Thursday.

"The FAA was in contact with U.S. carriers following the crash of Malaysian Air Flight 17," the agency said in a statement, hours after the Malaysian flight with 280 passengers and 15 crew members on board crashed in Ukraine near the Russian border.

"The FAA is monitoring the situation to determine whether further guidance is necessary," the agency added.

In April, the FAA issued a notice prohibiting U.S. flights to operate in the airspace over the Crimean region of Ukraine and near the Black Sea "due to the continuing potential for instability." However, this notice did not cover the airspace where the Malaysian plane went down.

U.S. carrier Delta Air Lines said in a statement Thursday that it is "not routing flights through Ukraine airspace" and is " monitoring the situation" involving the downed Malaysian flight.

Boeing also said in a statement that it "stands ready to provide assistance if requested by authorities."

U.S. President Barack Obama said Thursday it is the "first priority" for the United States to determine whether any Americans were on board the downed passenger plane.

"The United States will offer any assistance we can to help determine what happened and why," he said.

The Malaysian passenger jet that crashed near the Ukraine- Russia border was shot down by a surface-to-air missile, according to U.S. media.