Story highlights Russian military's damage assessments said only six MiG-23 planes were destroyed

Military analysts say Syria's airforce consists of more than 200 operational fighters

(CNN) The US airstrike on Syria's Shayrat airbase Friday destroyed about 20% of the Syrian government's operational aircraft, Secretary of Defense James Mattis claimed in a statement Monday.

"The Syrian government has lost the ability to refuel or rearm aircraft at Shayrat airfield and at this point, use of the runway is of idle military interest," Mattis said, describing the strike as a "measured response."

The updated assessment was released after US President Trump asked Mattis for more information on the extent of the damage to the airbase, according to a senior administration official.

The US fired 59 Tomahawk missiles at the Syrian airbase after more than 80 people were killed, including children , in chemical weapons attack in Idlib province.

"The Syrian government would be ill-advised ever again to use chemical weapons," Mattis said.