WASHINGTON — After scores of children were killed in a Saudi-backed air strike in Yemen last week, U.S. Sen. Elizabeth Warren is challenging the top U.S. commander for the Mideast to say whether the U.S. military can track the purpose, mission and results of airstrikes in Yemen it supports.

In response to the Saudi-led coalition bombing of a school bus that reportedly killed 51 people — 40 of them children — Warren sent a letter to U.S. Central Command’s Gen. Joseph Votel on Tuesday asking that he clarify his testimony the military cannot do detailed tracking.

Warren pointed to recent media reports contradicting that assertion, which found that U.S. military officials closely observed a series of strikes that appear, she said, inconsistent with strict legal standards for the prevention of civilian casualties.

"The reported presence of U.S. advisors in a command center responsible for actively approving and directing such airstrikes, and the reported existence of at least one U.S. intelligence assessment of an airstrike acknowledging the use of U.S.-manufactured munitions, raise questions about whether the U.S. does in fact have the capability to track the origins, purpose and results of U.S.-supported airstrikes should it choose to do so," Warren wrote.

The United States has provided munitions, aerial refueling, and other logistical support to Saudi Arabia's military operations in Yemen for more than three years. Saudi and Emirati forces are fighting Iranian-backed Houthi rebels.

Houthi officials called the school bus strike a "crime by America and its allies against the children of Yemen,” according to the BBC.

U.S. Special Forces are reportedly on the ground in Yemen advising anti-al-Qaeda fighters and calling in American airstrikes. Warren, amid other questions for Votel, asked whether U.S. ground troops were involved in the fight against Houthi rebels—and if so, what their legal authority is.

A member of the Senate Armed Services Committee and a likely presidential contender in 2020, Warren is among a growing number of Democrats, and some Republicans, questioning U.S. involvement in Yemen’s civil war, a mushrooming humanitarian disaster that’s led to thousands of deaths.

Warren, who is seeking answers to her questions by Aug. 30, is not the only Democrat pressing the issue after the school bus bombing.

House Democrats wrote to Defense Secretary Jim Mattis, Secretary of State Mike Pompeo and National Intelligence Director Daniel Coats to request a briefing about the U.S. involvement in the conflict.

And Rep. Ted Lieu, D-Calif., has asked the Department of Defense Inspector General to investigate whether U.S. personnel supporting the Saudi-led coalition were violating U.S. or international law.