About 10,000 Turkish soldiers have crossed into northern Iraq to attack Kurdish rebels, and the government said it might send forces into Syria to eradicate guerrilla bases there. Tension between Turkey and Syria has risen to the point where the top Turkish military commander says the two hostile neighbors have reached ``a state of undeclared war''. In a sign of Arab concern over growing tensions between Turkey and Syria, Egyptian President Hosni Mubarak flew on short notice to Syria on Sunday in an effort to defuse what is being portrayed in the Middle East as an unsettling crisis.