MOSCOW (AP) — Russian President Vladimir Putin has tacitly criticized a popular opposition leader whose efforts to expose official corruption fueled nationwide protests last month.

Putin didn't name Alexei Navalny, but the reference was clear. The president said Monday that it was important to differentiate between those who truly want to fight corruption and "strengthen the state" and those "who try to use it as a tool in their own political fight."

A month ago, Navalny organized the largest protests in years. He has announced plans to run for president in 2018, when Putin is widely expected to seek a fourth term.

Putin pointed to Ukraine, where protesters calling for an end to corruption ousted the president in 2014. Putin claimed corruption in Ukraine has only worsened under the new Western-aligned government.