Turkish artillery units and warplanes belonging to the US-led coalition also pounded Jarablus.
A US defense official told CNN the anti-ISIS coalition has conducted eight airstrikes in support of the Jarablus operation.
The strikes were conducted using unmanned and manned aircraft, including A-10s and F-16s. The fight includes US-trained fighters known as the Vetted Syrian Opposition and Turkish forces.
Strikes were conducted against ISIS fighters and mortar positions, the official said.
The United States believes the ISIS fighters in Jarablus number in the hundreds.
There are no US boots on the ground in Jarablus, said the US official, adding, "We've been in communication with the Turks about the operation."
The official said the campaign is "very significant."
"This is a critical location because of the foreign fighter flow" from Europe and elsewhere, as well as helping stem the flow of fighters leaving Syria and Iraq.
Another senior US official told CNN's Barbara Starr the US assessment is that Turkey's cross-border action is largely about trying to stop Kurdish action. "The Turks never cared about Jarablus until the Kurds wanted to get there," the official said.
The operation -- dubbed
according to Anadolu -- came two days after Turkish artillery units started shelling ISIS positions in Jarablus
. That followed a recent mortar attack on residential areas in Karkamis, a town on the Turkish side of the border.
The move also came after a bombing Saturday night in the Turkish city of Gaziantep, near the Syrian border, that killed 54 people at a wedding celebration
. That attack, which Turkey blames on ISIS, was the deadliest in a string of blasts across the nation this year.
Turkish Foreign Minister Mevlut Cavusoglu said his country will "fully support" operations against ISIS positions in Jarablus.
Troops will create a safe zone of 90 by 40 kilometers (55 by 25 miles) for refugees between the towns of Marea and Jarablus, Turkish media said.
Interior Minister Efkan Ala, in an interview with state media, said "we are working together with coalition and moderate opposition. Turkey will not allow terrorist organizations next to us to threaten Turkey. What is indispensable for Turkey is the territorial unity of Syria."
Meanwhile, US Vice President Joe Biden arrived Wednesday in Ankara, the Turkish capital, where he was to meet with Erdogan and Prime Minister Binali Yildirim.
Syrian government condemns move
The Syrian foreign ministry, representing a government that has lost territory to ISIS and other opposition groups in a five-year civil war, condemned "this blatant breach to its sovereignty" by Turkey, Syria's state news agency reported.
"Fighting terrorism on Syrian territory from any side should have been coordinated with Syrian government and the Syrian ... army that has been fighting in these battles for five years," the ministry said.
Turkey had vowed to eradicate ISIS from its border regions in the wake of Saturday's deadly bombing in Gaziantep.
"Our border must be completely cleansed of Daesh," Cavusoglu said in televised remarks Monday, referring to ISIS by another name.
Turkey's battle with Kurdish fighters
Turkey's government signaled that its offensive will not only target ISIS but also the Syrian Kurdish YPG -- the military wing of the Democratic Union Party, or PYD.
Turkey and the YPG share a common enemy in ISIS. Kurds are a large ethnic minority in Syria, and they have been a US ally in the fight against ISIS there, playing a major role in driving ISIS out of the northern Syrian city of Manbij
earlier this month.
But Turkey is determined to keep the Kurdish YPG fighters from establishing Kurdish control of the border area on the Syrian side should ISIS be pushed out.
Turkey says the YPG is linked to Turkey's own Kurdish insurgents, the outlawed Kurdistan Workers Party, or PKK, who have been blamed for deadly attacks in the country since a ceasefire crumbled last year.
Now that it's in Manbij, the YPG has its sights on the border city of Jarablus -- 40 kilometers (25 miles) to the north. The YPG has been eager to drive ISIS out and to remove the terror group's access to resupply of materiel and fighters from Turkey.
On Monday, even while Turkey fired artillery at ISIS in Jarablus, it also shelled YPG fighters north of Manbij.
Cavusoglu, the Turkish foreign minister, said his country wants the YPG to return east of Syria's Euphrates River. Both Manbij and Jarablus are west of the river.
"Otherwise, I am saying very clearly that we will do what is necessary," Cavusoglu said, according to Anadolu.
Yildirim, the Turkish Prime Minister, urged the United States to review its relationship with the YPG and the PYD.
"The US should know that at the end of the day, you might use a terrorist organization to defeat another one, but how are you going to be able to defeat the terror organization that's left in your hands?" Yildirim said Wednesday.