Correction, 11/6: A previous version of this article stated that Hassan Nasrallah made the comments during Imam al Khamanei conference. The conference is called the Conference of Renovation and Intellectual Jurisprudence of Imam Khamenei.
Dozens of fighters from the Islamic State of Iraq and the Levant group and at least nine fighters belonging to the Lebanese Hezbollah have reportedly been killed as the two sides clashed along the Lebanese border with Syria.
Hassan Nasrallah, Hezbollah's secretary-general, announced on Wednesday that the battle against ISIL has begun, stating the group started the fight but Hezbollah will continue it until the end.
"The fight with ISIL in Qalamoun has begun. They started by attacking us, but we are determined to put an end to this terrorist threat on our border," Nasrallah said in a televised speech.
"We renew our determination that we will no longer accept the continued presence and the threat of takfiris on our border and on our villages, and we are working calmly to achieve this goal."
The speech comes a day after clashes between the two groups began in earnest, with Hezbollah-affiliated TV station Al Manar reporting that ISIL had targeted several Hezbollah positions along the outskirts of the northeastern Lebanese border villages of al-Qaa and Ras Baalbak, but were repelled by the Lebanese group.
Al Manar aired footage of ISIL bases and dead fighters, stating that around 50 ISIL fighters were killed, and another 80 were injured.
The ensuing battle left scores of ISIL casualties, including the group's leader in the Qalamoun border region identified as Saudi national Walid Abdel Mohsen al-Omari, the channel said.
In his speech, Nasrallah said, "Great achievements were made in Qalamoun, especially the achievements made this morning," adding that the party had achieved huge victories in the area and that now "all the high mountain tops are now under the control of the Syrian Arab Army and Hezbollah".
According to Hisham Jaber, a retired Lebanese army general, the battle in Qalamoun is "a decisive battle for Hezbollah, and they will not stop until they have managed to remove the threat".
ISIL launched their attack because they wanted to catch Hezbollah off guard, "but they were unsuccessful because Hezbollah was prepared," said Jaber, adding that the ISIL fighters are in a weak position “because their supplies have been reduced significantly, and they can’t survive like this."
Hezbollah has been on the offensive in Syria's Qalamoun mountains for weeks and has recaptured territory that had been under the control of al-Qaeda's Syria branch, the Nusra Front, one of the more powerful armed groups currently fighting on the ground in Syria.
With the Nusra Front almost defeated in the area, a major battle was expected between Hezbollah and ISIL, who is positioned in the northern section of the Qalamoun mountain range.
The total area of the Qalamoun mountains that is being contested is about 1,000sq km - of which 340sq km lie in Lebanon and are under the control of ISIL fighters and the Nusra Front.
Nasrallah has stated several times in recent speeches that the party will not accept the presence of these armed groups along the Lebanese border as they pose a direct threat on Lebanese towns and villages, and if the government fails to accept the responsibility of protecting the country, Hezbollah will take on the role.
"A lot of this is a media propaganda war, which Hezbollah is pushing in order to make up for the losses they, along with the Syrian army, are facing in Syria," Mario Abou Zeid, a political and military analyst from Carnegie Middle East Center, told Al Jazeera.
"The threat from ISIL is exaggerated; they do not have the capability nor the support to expand into Lebanon. The real threat is from the Nusra Front, but right now they are focused on Damascus, so infiltrating Lebanon is not a priority at the present time."
"[Nusra Front leader Abu Mohammad] al-Joulani made it very clear that Hezbollah is their next target, so Nusra is definitely the most eminent threat to the country, because of Hezbollah."
On Tuesday, local media reports stated that Hezbollah and the Syrian army were able to regain control over half the area, making steady advances against the fighters who have been holed up in the mountains for the last year and a half.
Source: Al Jazeera and agencies