Turkish forces and some 10,000 Free Syrian Army militia based in Turkey would be facing even more difficulties if Russian Federation had not allowed Turkish jets to operate in Syrian airspace. The latter has been fighting for an autonomous region inside Turkey since 1984.
The operation is being carried out under the framework of Turkey's rights based on worldwide law, UN Security Council decisions, self-defense rights under the UN Charter and respect for Syria's territorial integrity, it said.
It sees the militia as an offshoot of the outlawed Kurdistan Workers Party (PKK) which has waged a bloody insurgency in southeastern Turkey since 1984.
According to estimates, there are between 8,000 to 10,000 Kurdish YPG fighters in the Afrin area.
The PKK, YPG and PYD consider as their guide the Kurdish Marxist-nationalist leader Abdullah Ocalan, who is imprisoned on a Turkish island for leading a separatist movement.
Mattis claimed that Turkey has "legitimate security concerns", while also praising the Kurds and other USA battlefield allies for their fight against the Islamic State (ISIS) in Syria. This has infuriated Ankara and strained its relations with Washington even though the two are North Atlantic Treaty Organisation allies. The YPG denies any direct links to the group.
The Syrian government, its ally Iran and Egypt have all condemned Turkey's offensive. In the eyes of Russia, Washington continues to "actively encourage" Kurdish separatism in Syria, Foreign Minister Sergey Lavrov said, adding that "the USA have long sought in many ways to discourage the Kurds from talking to Damascus".
The parties have agreed on "de-escalation zones", which has allowed Turkey to send troops to rebel-held Idlib province in October as a monitor. The Observatory said Turkey-backed troops were attempting once again to enter Afrin.
Lt. Cmdr. Rebecca Rebarich, a Pentagon spokeswoman, told CNBC in a written statement Monday: "We recognize Turkey's security concerns about the PKK, a USA -designated foreign terrorist organization".
U.S. Secretary of State Rex Tillerson insisted, however, that the Syria-Turkey border force report had been mischaracterized.
"Our investors should be at ease, the impact will be limited, the operation will be brief and it will reduce the terror risk to Turkey in the period ahead", he said.
This probably refers to Russian Federation agreeing to limited Turkish action as a warning to the Kurds not to become the permanent proxies of the USA in Syria.
The district of Afrin is home to around 500,000 civilians, including refugees from elsewhere in Syria. Airstrikes could lead to another humanitarian crisis.
This is especially true because Kurdish officials say they intend to launch a substantial counterattack against Turkey, and the SDF may decide they want to commit those forces to the battle sooner rather than later.
This was a risky new departure for the USA in Syria. Turkey's strong reaction led the USA to backtrack this plan but Washington's opposition against any Turkish military operation against the YPG casts a shadow on ties.
However, the Russian Defense Ministry put the blame for Turkey's "extremely negative reaction" fair and square on "the provocative United States steps aimed at the separation of regions with a predominantly Kurdish population" and "the Pentagon's uncontrolled deliveries of modern weapons to the pro-US forces in northern Syria".
"Donald Trump is tough, but Mattis is most heard in the Cabinet there because he is the wisest person, he is a tough soldier but he is wise", Ryamizard said. The two governments have been at odds for years.
He then spoke with generals at the Turkish General Staff and Turkish Land Forces' operating bases. Skirmishes in the east already have been reported.
Twenty-four people had been detained in other cities on Monday.