Turkish troops killed 20 Kurdish guerrillas on Sunday in a major operation against separatist rebels in eastern Turkey, army sources said.
The operation involved 8,000 troops with air support in the province of Tunceli, hundreds of kilometers (miles) from the Iraqi border. The sources gave no details on army casualties.
Ankara feels threatened by Kurdish separatists, especially those attacking from bases in mountainous north Iraq, and says it may still use a military solution to tackle these rebels.
The outlawed Kurdistan Workers Party (PKK) has killed about 40 people in a month, including 12 soldiers in the latest major attack, and said it took eight soldiers prisoner.
In Istanbul, police in riot gear and armored vehicles scuffled with demonstrators calling for the PKK's jailed leader to be freed and protesting against any incursion into Iraq.
Protesters hurled petrol bombs after some 200 people marched chanting through the streets.
In nearby Izmit, three people at an anti-PKK rally were lightly injured by an explosion, the state news agency Anatolian reported. Other demonstrations were held across the country.
Ankara is under strong domestic pressure to deal with the PKK, but Turkish-Iraqi talks aimed at preventing a cross-border ground incursion collapsed on Friday.
Turkey has massed up to 100,000 troops, backed by fighters, helicopter gunships and tanks on the border for a possible offensive against an estimated 3,000 rebels based in Iraq.
Alongside diplomatic initiatives, Turkey has used tough rhetoric to try to press the United States and Iraq into action. Prime Minister Tayyip Erdogan said on Saturday a military operation could be carried out whenever it was needed.
"The United States has the real responsibility. It should hand them (PKK) over to Turkey and cooperate. Neither the U.S. nor Iraq has done anything that satisfies Turkey so far," Deputy Prime Minister Cemil Cicek was quoted as saying on Sunday.
"We can use or continue to use diplomatic means, or resort to military means. All of these are on the table," Foreign Minister Ali Babacan said in translated comments on Iran's Press TV television channel, during a visit to Iran.
Ankara has demanded Iraq hand over Iraq-based members of the PKK, which is blamed for more than 30,000 deaths in a separatist campaign in mainly Kurdish southeast Turkey since 1984.
But Baghdad has little control over semi-autonomous northern Iraq run by the Kurdistan Regional Government, whose leader has vowed not to hand over anyone to NATO-member Turkey.
"I will not hand over any person to any regional state no matter the cost, however, in truth, I will not allow any PKK official to use the Kurdistan region as a base or to be present here and threaten the security of Turkey," Masoud Barzani said in an interview with Al Jazeera television aired on Sunday.
He has accused Turkey of using the PKK as a pretext to invade northern Iraq and undermine the Kurdish population there.
Kurds make up a fifth of Turkey's population and have long complained of discrimination. Rights have improved in recent years as Turkey negotiates European Union membership.
"Our target is not the Iraqi people or government. We do not have any imperialist intentions or we have nothing to do with oil," Anatolian news agency quoted Cicek as saying.
"Our target is the terrorist organization PKK."
Turkish President Abdullah Gul told Iranian President Mahmoud Ahmadinejad that diplomatic channels were being exhausted and Turkey was determined to root out the PKK from northern Iraq, Anatolian reported.
Ahmadinejad also told Iraq he supported a crackdown on the PKK but wanted a peaceful solution. Iran also has a Kurdish minority and has faced cross-border attacks by rebels, to which it has responded by shelling targets in Iraq.
The United States fears a major Turkish incursion could destabilize relatively peaceful north of Iraq.
Erdogan is due to visit President George W. Bush on November 5. Senior Turkish diplomats say Erdogan has given Washington and Baghdad a deadline for showing concrete results or steps to be taken on the Kurds and the Washington talks are the last chance.
(Additional reporting by Emma Ross-Thomas and Paul de Bendern in Istanbul, Ferit Demir in Tunceli, Andrew Marshall in Baghdad, Fredrik Dahl and Parisa Hafezi in Tehran)