Kurds across Turkey have vented their anger at the government's lack of military support for the defenders of the Syrian border town of Kobane being attacked by Islamic State militants.
Police used tear gas and water cannon as unrest spread to at least six cities. At least nine people died.
Turkish troops and tanks have lined the border but have not crossed into Syria.
Fresh US-led air strikes have tried to repel IS, but Turkey's president warned Kobane was "about to fall".
At least 400 people have died in three weeks of fighting for Kobane, monitors say, and 160,000 Syrians have fled.
If IS captures Kobane, its jihadists will control a long stretch of the Syrian-Turkish border.
At the scene: BBC's Paul Adams on Syria-Turkey border
This was a day of air strikes. From the early hours of the morning until late afternoon, great columns of black smoke rose from positions around Kobane.
The strikes didn't end the gunfire, but did seem to bring the advance by Islamic State to a juddering halt. At times the town seemed eerily quiet, certainly by contrast with Monday's furious assault.
For the first time, the air strikes seem to be making a difference. But sources inside Kobane are calling for more. They say the don't want Turkish troops to intervene but are pleading with Turkey to allow armed Kurdish fighters to join them. Of that, in public at least, there is absolutely no sign.
Protests spread across Turkey on Tuesday.
The authorities in the southern province of Mardin declared a curfew in six districts and a group of Turkish nationalists surrounded a building in Istanbul which Kurds had occupied.
One 25-year-old protester was killed in the eastern province of Mus.
Most of the other deaths were in Diyarbakir, Turkey's largest Kurdish city.
Some protesters accused Turkey's government of collaborating with IS.
The Kurdistan Workers' Party (PKK), the biggest Kurdish party in Turkey, called for members and supporters to take to the streets to protest against the IS offensive.
The PKK is seen as a terrorist group in Turkey, where decades of armed struggle against the Turkish government for self-determination has left both sides deeply mistrustful of each other.
The cities of Diyarbakir, Ankara, Mersin and Adana have also seen protests, and there have been others across Europe.
Dozens of demonstrators smashed a glass door and entered the European Parliament, where President Martin Schulz promised to discuss the situation with EU leaders.
Hundreds more protesters demonstrated in Berlin and other German cities.
Meanwhile, groups of Kurds reportedly intending to cross the Turkish border to head for Kobane were stopped by border police.
According to one witness, about 300 Kurds were stopped in the border town of Suruc.
Analysis: BBC's Mark Lowen in Istanbul
The crisis in Kobane is reawakening the ghosts of the civil war between Turkey and the Kurds.
While Islamic State tightens its grip on Kobane, Turkey is still holding fire on deploying troops. It remains reluctant to help the Kurdish militia in Syria, which has close links with Kurdish fighters here.
And the Turkish government has again called for the US-led coalition to target the Assad regime as well as IS - and for a no-fly zone to ease the refugee influx into Turkey. But neither goal seems within reach, the US state department reiterating that the air strikes remained focused on IS alone. The Kurds say Turkey's failure to act will lead to the fall of Kobane.
Turkish President Recep Tayyip Erdogan admitted on a visit to a refugee camp for Syrians that "right now, Kobane is about to fall".
He said: "We had warned the West. We wanted three things: no-fly zone, a secure zone parallel to that, and the training of moderate Syrian rebels."
Mr Erdogan said that "the terror will not be over... unless we co-operate for a ground operation", although he gave no further details.
Last week, Turkey pledged to prevent Kobane from falling to IS and its parliament authorised military operations against militants in Iraq and Syria.
But Kurds have accused Turkey of simply standing by as IS advanced on the Syrian Kurds defending Kobane.