Saudi Arabian coalition jets bombing Houthi rebel sites in Yemen increasingly turn to U.S. Air Force tankers for refueling support almost two years after the conflict began.

Since April 2015, the Air Force has logged 1,778 tanker sorties for the operation, Air Forces Central Command spokeswoman Capt. Kathleen Atanasoff told on Tuesday. That includes 1,069 over the past year, an increase of 360, or 50 percent, from the 709 in the previous period.

“These operations are ongoing, with aircraft refueling occurring daily,” Atanasoff said in an email.

The service’s tankers such as KC-135 Stratotankers and KC-10 Extenders participated in 7,564 refueling “events” with coalition aircraft, with “about 54 million pounds of fuel off-loaded in support of Saudi operations in Yemen,” Atanasoff said.

Refueling numbers are tracked by the command but, unlike statistics on strikes and sorties against the Islamic State and the Taliban, aren’t publicly released via the command’s airpower summary factsheets.

The Air Force’s involvement with Saudi airstrikes in Yemen drew scrutiny in October after one hit a funeral hall packed with mourners in Sanaa, killing more than 150 people and wounding hundreds, according to The New York Times. The incident prompted the U.S. to launch an immediate review of its support operations for the Saudi-led coalition, the Times reported.

U.S. Central Command officials have said the U.S. provides only refueling support to Saudi coalition aircraft. “We have not provided any kind of intel to carry out strikes,” Maj. Josh Jacques, media chief at CentCom, told at the time.

According to The Yemen Data Project, an independent body of researchers, academics and human rights advocates, more than 8,600 air attacks occurred between March 2015 and August 2016 in Yemen — with more than 3,150 hitting non-military locations, as cited by The Guardian.

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