Turkey and the United States hope that by removing Islamic State from the border, they can deprive it of a smuggling route which long saw its ranks swollen with foreign fighters and its coffers boosted by illicit trade.
But for Turkey, it also preempts any attempt by Syrian Kurdish militia fighters, who play a critical part of the U.S.-backed campaign against Islamic State, to take Jarablus.
Kurdish fighters have captured large areas of territory since the start of the Syrian conflict in 2011, and Ankara has long declared the Euphrates river, which runs just east of Jarablus, a red line which it does not want them to cross.
Foreign Minister Mevlut Cavusoglu said Kurdish fighters must return east of the Euphrates or Turkey would "do what is necessary". He said the operation was a turning point and would accelerate removing Islamic State from Syria's Aleppo region.
Plumes of smoke rose from the hills around Jarablus, visible from the Turkish town of Karkamis across the border. The boom of artillery rounds was audible as advancing Turkish tanks fired.
Turkish military sources said the air strikes had hit 12 Islamic State targets, while artillery fire hit 70 targets.
"The aim of the operation is to ensure border security and Syria's territorial integrity while supporting the U.S.-led coalition against Islamic State," one military source said, adding work to open a passage for ground forces was under way.
Saleh Muslim, head of the Kurdish PYD, wrote in a tweet that Turkey was entering a "quagmire" in Syria and faced defeat there like Islamic State. Redur Xelil, spokesman for the Syrian Kurdish YPG militia, said the intervention was a "blatant aggression in Syrian internal affairs".
Kurdish groups control swathes of northern Syria where they established de facto autonomy since the start of the Syria war. The YPG, armed wing of the PYD, took control of most of Hasaka city on Tuesday, about 250 km (155 miles) east of Jarablus.
That growing Kurdish influence has alarmed Ankara, which is fighting its own insurgency with militants from the outlawed Kurdistan Workers Party (PKK), blamed by the government for an escalation of attacks in the southeast of Turkey.
The U.S.-backed Syria Democratic Forces alliance (SDF), which includes the YPG, captured the city of Manbij, just south of Jarablus, from Islamic State earlier this month.
The U.S. official acknowledged Turkey had not been happy about the Manbij operation but said Washington underlined the Kurds would pull back once the city was cleared and that they would not move north, addressing a major Turkish concern.
"We've put a lid on the Kurds moving north, or at least doing so if they want any support from us," he said.
Turkey had vowed on Monday to "completely cleanse" Islamic State militants from its border region after the Gaziantep bombing. Operation "Euphrates Shield" also comes after at least 10 mortar shells from Jarablus landed in Karkamis and the surrounding areas in recent days, forcing residents to flee.
Syrian rebels backed by Turkey had said they were in the final stages of preparing an assault from Turkish territory on Jarablus. A Syrian rebel with one of the Turkey-backed groups said about 1,500 fighters had gathered in Turkey to take part.
It is Turkey's first major military operation since the failed July coup by rogue soldiers who tried to overthrow Erdogan and the government, killing 240 people and triggering a purge of suspected coup supporters in the army and civil service.
Angered by a perceived lack of Western sympathy over the coup, Turkey chilled ties with Washington and the EU while ending a diplomatic row with Russia and proposing more military cooperation with Moscow in fighting Islamic State. Growing ties between Ankara and Moscow have worried Turkey's Western allies.