There's no question that free speech has been under attack across the globe in 2015.

The year started off with the mass killing of editorial staff at the Paris headquarters of satirical newspaperCharlie Hebdo. Most recently, Russian opposition leader Boris Nemtsov was shot dead near the Kremlin in Moscow.

Globally, at least 17 journalists have been killed in 2015, according to the Committee to Protect Journalists.

The trend appears to be continuing from previous years.

"The total number of deaths in 2014 demonstrates the sustained level of risk to journalists over the past decade," CPJ's news director Shazdeh Omari wroteof last year's numbers. "The past three years are the most deadly period CPJ has recorded."

From social media censorship to crackdowns on political dissent, governments and militant groups alikecontinue to target voices they disagree with. Writers, cartoonists, photographers, filmmakers, bloggers, protesters and opposition figures can all become targets.

Here are the main incidents that have already made headlines in the first months of 2015.

France

On Jan. 7, 12 people, most of them editorial staff, were gunned down at and near the Charlie Hebdo offices in Paris. Al Qaeda in the Arabian Peninsula claimed responsibility for the shootings, which were carried out by brothers Said and Cherif Kouachi. A third gunman and friend of the Kouachis, Amedy Coulibaly, killed four hostages at a kosher market two days later in what appeared to be a related attack. Video later emerged that showed Coulibaly declaring allegiance to the Islamic State.

The string of killings amounted to the worst terror attack on French soil in 50 years. The assault on Charlie Hebdo was widely seen as targeting free speech; the weekly paper is known for running offensive and provocative content, including depictions of the Muslim Prophet Muhammad.

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2015 is proving to be another deadly year for free speech