Ankara was cautioned against sending troops into Iraq but was said, that the European Commission supported Turkey.
The EU appeal came as dozens of Turkish military vehicles headed toward the Iraqi border on Monday and protesters demanded tough action against Kurdish rebels. A rebel ambush killed 12 Turkish soldiers on Sunday, pushing Turkey closer to a possible attack on guerrilla bases in northern Iraq.
"The European Commission expresses its solidarity with Turkey in the fight against terrorism, which is a common challenge for the EU and Turkey," EU Enlargement Commissioner Olli Rehn said in a brief statement issued in Brussels.
Rehn, the EU's point man in relations with EU membership candidate Turkey, said the EU understands Turkey "faces continual cross-border attacks from the PKK, which is on the EU list of terrorist organizations, (and) understands Turkey's need to protect its citizens."
Yet, it wants to see Turkey and Iraq "tackle this problem through cooperation ... and by respecting international law," Rehn said.
A drone video shows a Russian flag flying over the outermost house in the west of the city.