By Daren Butler
ISTANBUL (Reuters) - Turkish President Tayyip Erdogan upbraided the United States for its support of Syrian Kurdish rebels on Wednesday, saying Washington's inability to understand the group's true nature had turned the region into a "sea of blood".
Erdogan's comments, a day after Turkey summoned the U.S. ambassador over its support for the Syrian Kurds, illustrate Ankara's growing frustration with its NATO ally, which backs Syrian Kurdish rebels in the battle against Islamic State.
Adding to the tension, the army said one Turkish soldier was killed and another wounded when security forces clashed with Kurdish militants crossing over from Syria.
Ankara sees the Syrian Kurdish PYD as terrorists, citing their links to the Kurdistan Workers Party (PKK), which has carried out a violent, three-decade insurgency for Kurdish autonomy in Turkey's southeast.
"Are you our side or the side of the terrorist PYD and PKK organization?" Erdogan said in a speech in Ankara to provincial officials.
He added that Washington's inability to grasp the nature of the two groups had caused a "sea of blood" and created a domestic security issue for Turkey.
Ankara summoned the U.S. ambassador to express its displeasure after State Department spokesman John Kirby said on Monday the United States did not regard the PYD as a terrorist organization.
As well as battling both a Kurdish insurgency and Islamic State, Turkey has been grappling with an influx of more than 2.5 million refugees since the start of the Syrian civil war.
Turkey's spending on the Syrian refugee crisis has reached $10 billion, while the United Nations has given just $455 million, Erdogan said.
Turkish soldiers spotted seven PKK militants entering Sirnak province's Cizre district from Syria on Tuesday evening and, as they clashed, one soldier was killed and one wounded, the Turkish armed forces said.
In another incident, one police officer was killed and another wounded when PKK rebels launched a rocket attack on an armored vehicle in the town of Sirnak, state-run Anadolu Agency reported. It was not clear when that attack occurred.
Military sources said the army seized up to 15 kg of explosives and four suicide-bomber vests when it detained 34 people trying to cross into Turkey from an area in Syria under Islamic State control.
The area of Syria near where the soldiers clashed is controlled by the Kurdish Democratic Union Party (PYD).
Turkey fears that the advances by Syrian Kurds against Islamic State on its 900-km (560-mile) border with Syria will fuel separatist ambitions among its own Kurds.
A ceasefire between the PKK and the government collapsed in July following what the government said were attacks on security forces, plunging southeast Turkey into its worst violence since the 1990s and scuppering peace talks.
The PYD and the PKK share not only ideology but fighters, with the PKK drawing Syrian Kurdish fighters to its camps in northern Iraq and Turkish Kurds serving among the PYD ranks.
(Additional reporting by Tulay Karadeniz in Ankara and Ayla Jean Yackley and Asli Kandemir in Istanbul; Writing by David Dolan and Daren Butler; Editing by Andrew Heavens)