An Istanbul court on Thursday sentenced two prominent Turkish journalists to two years behind bars for illustrating their columns with a cartoon of the Prophet Mohammed originally published by French satirical weekly Charlie Hebdo.

The sentence handed to columnists Hikmet Cetinkaya and Ceyda Karan, both columnists with the opposition Cumhuriyet daily, intensified alarm over press freedoms in Turkey under strongman President Recep Tayyip Erdogan, who has made Islam the cornerstone of his politics.

A woman suicide bomber on Wednesday blew herself up in the Turkish city of Bursa, killing herself and wounding at least 10 people, local media reported.

The attack took place near the city's 14th century Grand Mosque, a historic symbol of the northwestern city, the private CNN-Turk television reported.

Prime Minister Ahmet Davutoglu vowed Wednesday that Turkey's draft constitution would guarantee secularism, after calls for a religious charter sparked controversy in the predominantly Muslim country.

"Secularism will feature in the new constitution we draft as a principle that guarantees citizens' freedom of religion and faith and that ensures the state is at an equal distance from all faith groups," Davutoglu said in a televised speech.

Dutch Foreign Minister Bert Koenders has warned the Netherlands cannot guarantee the safety of citizens traveling to Turkey if they have been critical of Turkish leaders.

The warning, made during a parliamentary debate on Tuesday, comes as the Dutch government is working to lift a travel ban on Dutch-Turkish journalist Ebru Umar who was briefly arrested over the weekend for tweeting comments critical of President Recep Tayyip Erdogan.

Six Turkish sailors kidnapped early this month from aboard their vessel off the coast of Nigeria have been released unhurt, a maritime consultancy firm said on Tuesday.

Pirates attacked the merchant tanker used for crude oil operations on April 11 while it was steaming through the oil-rich Niger Delta and seized the sailors, including the captain.

Turkish police on Tuesday fired tear gas to disperse demonstrators who had gathered outside parliament to protest a call for the country to adopt a religious constitution.

Police broke up a group of more than 100 protesters, preventing them from making a press declaration outside the parliament in Ankara, an AFP photographer reported.

Turkey has struck a deal with the United States to deploy American light multiple rocket launchers on its border with Syria to combat the Islamic State group, according to the foreign ministry.

The High Mobility Artillery Rocket System (HIMARS) "will be deployed on the Turkish border in May as part of an agreement" with Washington, Foreign Minister Mevlut Cavusoglu said in an interview published Tuesday.

Hasnain Kazim, German news weekly Der Spiegel's resident correspondent in Turkey, last year applied to renew his Turkish press card -- usually a mere formality.

But when he had no reply, he knew something was wrong. Three months later, with no way to work without the card, he was forced to leave Turkey -- just one of a growing number of foreign journalists who believe the authorities are pushing them out.

Can Dundar, editor-in-chief of Turkey's leading opposition daily Cumhuriyet, was fined nearly 9,000 euros Monday for "insulting" President Recep Tayyip Erdogan when he was prime minister.

Dundar, who is currently standing trial along with his Ankara bureau chief on allegations of espionage, said on Twitter that the court-ordered fine would not stop him reporting.

Two people suspected of links to the Islamic State group and accused of planning an attack against "state dignitaries" have been arrested in Turkey ahead of a visit by top EU officials, local authorities said Saturday.

The arrests took place overnight in Konya, in the center of the country, as Turkey prepared for a visit by European Council head Donald Tusk and German Chancellor Angela Merkel in Gaziantep, which borders Syria and territories controlled by IS.