Several protesters threw punches at Republican People's Party leader Kemal Kilicdaroglu at the funeral outside Ankara on Sunday. Kilicdaroglu was not injured.
Interior Minister Suleyman Soylu said Monday nine people were detained for questioning.
The soldier was killed Saturday in clashes with Kurdish rebels. Soylu appeared to justify Kilicdaroglu's assault by referring to the support a pro-Kurdish gave the opposition during Turkey's March 31 municipal elections.
Soylu said: "Everyone must take sides against the (rebels)."
The Republican People's Party won the mayoral elections in Ankara and Istanbul, supplanting President Recep Tayyip Erdogan's party.
Erdogan led a divisive campaign, equating opposition parties with terrorists.
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