Turkey had threatened to launch a military operation against the Syrian Kurdish forces in a bid to claim Syrian territory.
The Turkish army has confirmed "launched the land operation into the east of the Euphrates river" adding it had hit 181 "militant targets".
The Syrian Foreign Ministry condemned the Turkish military offensive on Kurdish positions in northern and northeastern Syria, saying the Syrian government is determined to confront "Turkish aggression by all means".
Briefing a small group of journalists on Thursday, Mevlut Cavusoglu said Turkish troops and Syrian opposition fighters would be strengthened with more security force officers, including police, if needed.
And the Arab League, consisting of 22 states, is to hold an emergency meeting in Cairo on October 12 to discuss Turkey's assault.
He has said he would like the USA to negotiate a truce between North Atlantic Treaty Organisation ally Turkey and the Kurds.
On Thursday, Turkish police began criminal investigations of several Kurdish lawmakers and detained scores of people in the southeastern city of Diyarbakir, accusing them of criticising the military's incursion into Syria, state media reported.
The operation dubbed "Peace Spring" by the Turkish government, began on Wednesday at around 4 p.m. with air raids and shelling while a ground offensive, involving Turkish soldiers and allied Syrian rebels, began at 11.30 p.m., reports Efe news.
Turkey's offensive - named Operation Peace Spring - came after Trump agreed to withdraw American troops, paving the way for an assault on Kurdish forces that have always been allied with the United States in the fight against Islamic State in Iraq and Syria (ISIS).
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Turkey deems the YPG the Syrian offshoot of the illegal PKK, which is listed as a terrorist organization also by the United States and the EU.
Mr Trump's decision to have American troops step aside in north-eastern Syria was a major shift in United States policy and drew opposition from all sides at home.
In response to the Turkish incursion into northern Syria, the YPG fired mortar rounds into Turkish towns across the border and attacked Turkish-backed factions of the Free Syrian Army - recently rebranded as the Syrian National Army - Tel Rifat and Jarablus.
"The Syrian Kurds, including the 300,000 exiles in Turkey, are under Turkish protection". They reportedly include Zehra Duman, who fled Australia as a teenager to marry an Islamic State militant. He said he expected Turkey to protect civilians and religious minorities and prevent a humanitarian crisis - as Turkey has said it would.
Russian Federation said it planned to push for dialogue between the Syrian and Turkish governments following the incursion.
Trump also appeared open to discussions of bipartisan legislation on sanctions against Turkey, sponsored in part by his ally Sen.
The bill would likely freeze USA assets of the top Turkish politicians and impose visa restrictions on officials.
Ankara insists the long-planned operation is created to protect citizens from a security threat posed by Kurdish fighters who it views as terrorists even though they fought alongside USA troops in a bloody and hard-won ground campaign against ISIS in which they lost around 11,000 personnel.
"We urge restraint and call on all parties to the conflict in Syria to avoid escalatory or opportunistic actions that cause further instability and humanitarian suffering".