Some 1,500 Turkish-backed Syrian rebels are thought to be in the Turkish town of Gaziantep waiting to attack.
A bomb attack on a wedding there killed 54 people on Saturday.
Turkey also shelled positions at Manbij held by Kurdish YPG fighters, who have been advancing against IS.
The BBC’s Mark Lowen in Gaziantep says the attack in the city, blamed on IS, may have been spurred by reports of the imminent Syrian rebel offensive.
Why Turkey shelled both IS and the Kurds
Early on Tuesday, Turkish artillery fired at least 40 shells at IS positions in the Jarablus area after two mortar bombs landed in the Turkish town of Karkamis, just across the border, Turkish media report.
Nobody was hurt in the attack on Karkamis.
Turkish Foreign Minister Mevlut Cavusoglu has said IS should be “completely cleansed” from northern Syria.
Monday also saw Turkish shelling of IS positions but equally the bombardment of Kurdish YPG positions in the Manbij area.
A Turkish official quoted by Reuters news agency said artillery had fired on the Kurds 20 times.
“The fundamental aim in the latest operation is to open a corridor for moderate rebels,” the official said.
The YPG has been at the forefront of the recent advance against IS in northern Syria, leading the liberation of Manbij this month and driving the jihadists towards Jarablus.
Who are the 1,500 fighters in Gaziantep?
The fighters poised to enter Syria from Gaziantep are believed to be Turkish-backed Syrian rebels.
A senior rebel official quoted by Reuters said they were fighting under the banner of the Free Syrian Army.
It is believed that any such operation would be aimed at frustrating any further advance by the Kurds.
The Kurds themselves have non-Kurdish Syrian allies, fighting alongside the YPG under the banner of the Syrian Democratic Forces.
How the wedding attack in Gaziantep is connected
The identity and motive of the suicide bomber who attacked the wedding party have yet to be revealed.
Soon after the attack, President Recep Tayyip Erdogan said IS was the likely perpetrator but Prime Minister Binali Yildirim said on Monday that investigators actually did “not have a clue”.
He downplayed earlier reports that the attacker was an adolescent, saying this could not be confirmed.
What is known is that it was a Kurdish wedding and IS have targeted Turkish Kurds in the past.
Many of the victims were children as young as four.
Sixty-six people are still in hospital, 14 of them in a serious condition, Turkey’s Dogan news agency reported.
A disproportionately large number of women and children were killed in the attack because it targeted henna night, a part of the celebration attended mainly by women and children, says BBC Monitoring’s Turkey analyst Pinar Sevinclidir.
Where is Assad in all this?
Syrian government forces are not directly involved in the battle for the border at Jarablus, having gradually lost ground in the north over more than five years of civil war.
Turkey’s long-time position has been that President Bashar al-Assad must be ousted as a condition for peace in Syria.
However, Prime Minister Yildirim acknowledged this week that he was one of the “actors” and suggested he could play a role in an interim leadership.