This picture taken on August 24, 2016 shows Turkish army tanks standing by in the Turkish Syrian border city of Karkamis, in the southern region of Gaziantep (AFP)
Turkish tanks backed by fighter jets and special forces rolled into Syria Wednesday in an unprecedented operation to drive Islamic State (IS) militants out of a key Syrian border town.
The air and ground operation also involving Syrian fighters -- the most ambitious launched by Ankara in the Syria conflict -- is aimed at clearing Islamist militants from the town of Jarabulus directly opposite Turkey.
But President Recep Tayyip Erdogan emphasised the operation was also targeting Kurdish militia fighters opposed by Ankara who had also been closing in on IS-held Jarabulus.
The operation -- named "Euphrates Shield" -- began around 4:00am local time (0100 GMT) with Turkish artillery pounding dozens of IS targets around Jarabulus, the prime minister's office said.
Turkish F-16 fighter jets, backed by international coalition war planes, also hit targets inside Syria. An AFP photographer saw around a dozen Turkish tanks cross into Syria in support of Syrian opposition fighters.
Tensions had flared across the Syria-Turkey border the previous day following rocket fire from Jarabulus which landed inside Turkey, with the Turkish army firing howitzer rounds in response.
As well as tanks, the AFP photographer in the area of Karkamis opposite Jarabulus saw several smaller military vehicles believed to be carrying pro-Ankara Syrian rebels.
Foreign Minister Mevlut Cavusoglu confirmed the Syrian fighters had crossed from Turkey into Syria and the state-run Anadolu agency said they were now three kilometres (two miles) inside the border.
Security sources quoted by Turkish television said a small contingent of special forces had travelled into Syria to secure the area before a possible larger ground operation.
Turkish authorities had late Tuesday ordered the evacuation of Karkamis for safety reasons, raising expectations that an offensive was imminent.
Air strikes by Turkish jets also echoed through the skies, the photographer said. The effects of one air strike on the northern outskirts of Jarabulus were easily visible, sending up a cloud of black smoke and sand.
Turkey will want to show with the operation that it is serious about taking on IS, which has been blamed for a string of attacks inside the country, the latest a weekend attack on a Kurdish wedding in Gaziantep that left 54 dead.
Ankara was long accused of turning a blind eye to the rise of IS in Syria and even aiding its movements to-and-fro across the border, claims the government had always vehemently denied.
The launch of the operation comes as US Vice President Joe Biden arrived in Ankara to meet Erdogan, with agreeing a unified strategy on Syria set to be a crucial issue.
Biden is likely to face expressions of alarm from Turkey about the activities inside Syria of the People's Protection Units (YPG) militia, which Washington sees as an ally but Ankara regards as a terror group.
Saleh Moslem, the head of the Democratic Union Party (PYD), the YPG's political wing, tweeted that Turkey was now in the "Syrian quagmire" and would be "defeated" like IS.
Erdogan said the operation was aimed against both IS and PYD -- "terror groups that continuously threaten our country in northern Syria."
"We have said 'enough is enough' ... This process began from 4:00 am. This now needs to be resolved," said Erdogan.
The air strikes by Turkish F-16s were the first since a November crisis with Russia sparked when the Turkish air force downed one of Moscow's warplanes.
A dozen IS targets were completely destroyed in the air strikes. Turkish artillery meanwhile destroyed 70 IS targets, according to Turkish television.
The incursion by Turkish forces is the first such into Syria since February 2015, when hundreds of Turkish troops crossed the border to move the relics of the grandfather of the founder of the Ottoman Empire.
The movements have come at a critical juncture for Turkey in Syria's five-and-a-half-year war, with signs growing it is on the verge of a landmark policy shift.
Ankara has always called for the removal of President Bashar al-Assad, putting Turkey at odds with his main supporters Iran and Russia.
However Prime Minister Binali Yildirim acknowledged at the weekend for the first time that Assad was one of the "actors" in Syria and may need to stay on as part of a transition.
Turkey has been shaken by one of the bloodiest years in its modern history, with a string of attacks by IS militants and Kurdish militants and the botched July 15 coup.
The attack Saturday in Gaziantep on a wedding party for a young couple has horrified the country, with the majority of the 54 victims aged under 18 and including children as young as four.