PKK-linked groups carried out attacks on the Turkish Embassy in Brussels as well as three mosque buildings in Germany on Sunday, adding new incidents to the growing list of violent attacks on Turkish establishments in Europe.

A group of 10 to 12 people said to be linked to the PKK terrorist group doused the Turkish Embassy and Consulate General buildings with paint in Brussels. Diplomatic sources said the assailants threw red paint on the front area of the buildings. Police officers arrived after the incident to investigate.

Attacks on buildings affiliated with Turkey and Turkish organizations in Europe have intensified after Turkey launched Operation Olive Branch on Jan. 20 to remove the Syrian affiliate of the PKK, Democratic Union Party (PYD) and its People's Protection Units (YPG) militia, from Afrin in northwestern Syria. The operation is being carried out in line with Turkey's rights based on international law, U.N. Security Council resolutions, its self-defense rights laid out in the U.N. Charter and respect for Syria's territorial integrity.

At least three mosques have been vandalized in Germany. In the first incident, a mosque in the central city of Kassel was attacked with Molotov cocktails in the early morning. The attack only caused minor damage to the mosque, which is managed by the European Turk Union (ATB), one of the largest Muslim-Turkish associations in the country.

Security footage showed four assailants breaking some windows of the Yunus Emre Mosque. Frames were partially burned and walls were damaged. The incident took place at around 4:30 a.m. local time. Mustafa Koç, head of the cultural center that runs the mosque, said: "We want police to catch everyone responsible for the attack. The continuation of such attacks increases our worries. We expect authorities to move and act urgently solve these problems. We call on the whole Turkish community to remain prudent."

Separately on Sunday, two other mosques were vandalized in Herne and Amberg. Both are managed by the Turkish-Islamic Union for Religious Affairs (DİTİB).

At the Wanne Eickel Hacı Bayram Mosque, the vandals drew a cross on the front door and wrote messages praising Hitler. Political messages supporting the YPG and PKK terrorist group were spray painted on Ulu Mosque.

At least 40 such attacks have been recorded since the beginning of this year in Germany. The PYD, PKK and far-left organizations have claimed responsibility for more than two dozens attacks since launch of the Turkish military-led Operation Olive Branch in Afrin against the YPG.

The attacks targeted Turkish mosques, associations and shops in various cities, including Berlin, Frankfurt, Hamburg and Aachen.

German police have failed to identify the assailants in most of the incidents. The PKK has been banned in Germany since 1993, but it remains active with nearly 14,000 followers in the country. Ankara has long criticized Berlin for not taking serious measures against the PKK, which uses the country as a platform for fundraising, recruitment and propaganda.

The YPG in Syria has been supported military by the U.S. in the fight against Daesh, despite Ankara's warnings that its links to the PKK constitute a national security threat to Turkey and Syria's national integrity. The operation in Afrin was launched to eliminate security threats posed to Turkey from northern Syria.

In an opinion piece published in the Tagesspiegel newspaper, Germany's former Foreign Minister Sigmar Gabriel reiterated the U.S. administration's strategic mistake in Syria by supporting the YPG, despite legitimate security concerns from NATO ally Turkey.

"It seems that the U.S. evaluates the current tensions with Turkey as something temporary which can be contained, or it has lost sight of the geo-strategic role of Turkey," Gabriel said.

"The first assessment would be a mistake. The second would have disastrous consequences, especially for us Europeans," he said. "Turkey's Afrin operation is a message to the U.S.," and that Ankara seemed to be ready to pay any cost to prevent the PKK and YPG from taking control of areas bordering Turkey.

The Social Democratic Party (SPD) politician, who served as foreign minister in Chancellor Angela Merkel's previous coalition government, warned that the U.S.'s failure to address Turkey's concerns over the YPG and growing alienation between the two NATO allies would serve Russia's interests.