"The FA, Premier League and Football League are currently working together on the issue of flares, in conjunction with the Fire Service and St John Ambulance, in an effort to alert supporters to the potential dangers."
In a statement, the Premier League said: "Flares are extremely dangerous. They burn at close to 2,000 degrees and we have been made aware of several incidents where fans have sustained injuries by igniting them.
"They also generate such large quantities of smoke that they negatively impact on people's enjoyment of the game and can cause panic and breathing difficulties for fans sat close to them.
"We will be stepping up our work with supporter groups to help fans understand the dangers involved with flares and encourage the minority who are putting others at risk to stop using them."
United have yet to receive any complaints from their supporters following the incidents during the Liverpool game, but believe every effort was made to prevent such issues, including enhanced security, clear warnings against the use of flares and increased segregation.