President Trump spoke with Russian President Vladimir Putin on Monday to offer his sympathies following the crash of a Russian airline’s plane over the weekend.

Just after takeoff, Saratov Airlines Flight 703 crashed near Moscow on Sunday, killing all 71 passengers aboard the aircraft. The cause of the crash has yet to be determined.

Trump told Putin the U.S. would support Russian authorities as they conduct an investigation concerning the crash.

Trump and Putin addressed other areas of concern such as North Korea, according to a statement from press secretary Sarah Sanders.

“President Trump reiterated the importance of taking further steps to ensure the denuclearization of North Korea,” the statement said.

North Korea ramped up its nuclear weapons and missile programs in 2017, Trump's first year in office, despite international pressure and sanctions designed to convince Pyongyang to stop.