Attack helicopters buzzed over a hilly region in southeastern Turkey looking for Kurdish rebels after troops reportedly killed 15 separatist guerrillas in a morning operation.

The fighting occurred Sunday in the predominantly Kurdish province of Tunceli — far removed from the border with Iraq where most recent clashes have broken out — as the government pressed on with its efforts against guerrillas from the Kurdistan Worker's Party, or PKK.

Prime Minister Recep Tayyip Erdogan called for unity between Turks and his country's minority Kurds, but reiterated his government's determination to fight Iraq-based separatist Kurdish rebels.

"As long as we are firmly bound together, the treacherous separatist terrorist attacks will never reach their goal," Erdogan said Sunday in a message before Oct. 29 celebrations marking the 84th anniversary of the Turkish republic.

"I want to declare this one more time: the struggle we lead against the separatist terrorism that aims to destroy our unity and our constitutional order will continue with belief and determination," he said.

A 15-kilometer (9-mile) race across Istanbul's Bosporus bridge to the European side of the city turned into an anti-PKK protest Sunday, with thousands of runners waiving Turkish flags and shouting slogans denouncing the rebels.

"Down with the PKK" and "Every Turk is born a soldier," they shouted.

But riot police cracked down quickly on a pro-PKK rally in the poor Okmeydani neighborhood of Istanbul, shooting tear gas into the crowd and dispersing the 150 demonstrators. Some young men then threw rocks at police before running away into side streets.

PKK fighters have killed at least 42 people in the past month. Those casualties included some 30 Turkish soldiers in two ambushes that were the boldest attacks in years — increasing domestic pressure on Erdogan to act.

Turkey has demanded the extradition of PKK leaders, and has otherwise been threatening to stage a cross-border military offensive into Iraq to hunt down the rebels themselves.

The United States, Iraq and other countries have been pressing for Turkey to refrain from cross-border military operations. Such a campaign could derail one of the few stable areas in Iraq, and leave the United States in an awkward position with key allies: NATO-member Turkey, the Baghdad government and the self-governing Iraqi Kurds in the north.

The crisis was taking its toll on economic links between Turkey and Iraq, amid reports that Turkey is considering economic penalties because of Iraq's failure to crack down on the PKK.

Turkey's Deputy Prime Minister Cemil Cicek said Sunday that it was the responsibility of the U.S. troops in Iraq to crack down on the PKK rebels.

"The United States has not carried out measures that satisfy us, that satisfy the Turkish people," he said in an interview with Kanal 7 television.

The top American commander in Iraq, Gen. David Petraeus, refused to discuss any U.S. military involvement in the standoff but assured reporters at a U.S. base near Tikrit that the United States was involved.

The comments seemed aimed at allaying Turkish frustration, piqued on Friday when the American military commander in northern Iraq said he planned to do "absolutely nothing" to counter Kurdish rebels operating from the region.

U.S. Maj. Gen. Benjamin Mixon said it was not the U.S. military's responsibility to act, adding he had sent no extra American troops to the area, and was not tracking PKK hide-outs or logistics activities.

Mixon handed over regional command to Maj. Gen. Mark Hertling on Sunday as scheduled. After the ceremony, Hertling told reporters that it would be "inappropriate" for him to discuss possible military measures while "diplomatic efforts are ongoing."

Before the fighting in Tunceli, the Turkish military blocked roads into the region with armored personnel carriers and soldiers. By afternoon, long lines of trucks were backed up waiting to get through.

Tunceli is some 550 kilometers (340 miles) northeast of the province of Sirnak and 650 kilometers (400 miles) northeast of the province of Hakkari, the places where most of the recent fighting with the rebels has taken place. Sirnak and Hakkari border Iraq.

Fifteen rebels were killed in the operation, according to the private Dogan news agency, which was at the scene.