Tensions had flared across the Syria-Turkey border the previous day.
Turkish tanks on Wednesday approached the Syrian border and were firing on targets, but stopped short of crossing the frontier, CNN Turk reported, showing live footage of several tanks manoeuvring along the border. Earlier, CNN Turk said the tanks were crossing into Syria but then reported they had remained within Turkish territory.
Turkish fighter jets, backed by US-led coalition aircraft, struck Islamic State targets near the border town of Jarablus in Syria and tanks fired on the rebel positions with cross-border fire, military sources said.
Tensions had flared across the Syria-Turkey border the previous day, with Turkish forces pounding jihadists with artillery strikes following rocket fire from the Syrian town of Jarablus.
"The Turkish Armed Forces and the International Coalition Air Forces have launched a military operation aimed at clearing the district of Jarablus of the province of Aleppo from the terrorist organisation Daesh," the prime minister's statement said, using an Arabic acronym for the IS group.
The state-run news agency Anadolu said the operation began at around 4:00 am local time.
In an earlier interview with private NTV television, Deputy Prime Minister Numan Kurtulmus said Ankara saw Jarablus -- which lies opposite the Turkish town of Karkamis -- "as a national security matter". "What we have said, since the beginning, is that having Jarablus or any other city held by IS is unacceptable," he said.
The launch of the operation comes the day US Vice President is due in Ankara to meet Turkey's leadership, with agreeing on a unified strategy on Syria set to be a crucial issue. He is by far the highest-ranking Western official to visit Turkey since the coup attempt to unseat President Recep Tayyip Erdogan.
Turkish F-16 jets dropped bombs on IS targets in Jarablus, the private NTV television reported, in the first such assaults since a November crisis with Russia that was sparked when the Turkish air force downed one of Moscow's warplanes.
Security sources quoted by Turkish television said a small contingent of special forces travelled a few kilometres into Syria to secure the area before a possible operation.
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 ouster of President Bashar al-Assad as the key to ending the conflict, putting Turkey at odds with his main supporters Iran and Russia. However Prime Minister Binali Yildirim at the weekend for the first time acknowledged 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 jihadists and Kurdish militants and the botched July 15 coup.
With inputs from AFP/Reuters.
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