Lebanon’s Shiite Hezbollah movement threatened Wednesday to retaliate against Israel for carrying out an airstrike against one of the group’s positions in Lebanon for the first time in eight years, raising the stakes in Syria’s steadily expanding war.

Commenting publicly for the first time on the attack, which was reported Monday night by the Lebanese army, Hezbollah said the “Israeli enemy” had struck a position belonging to the group’s fighters in the Janta area in the Bekaa Valley.

“This new attack is a blatant act of aggression against Lebanon and its land,” Hezbollah said in a statement posted on its Web site, offering the first confirmation that Israel had struck a target inside Lebanon. The Lebanese army’s report left it unclear whether the strike had occurred on the Lebanese side of the border or the Syrian side.

Hezbollah said it would “choose the right time and place and the proper way to respond,” using language that suggests it does not plan to retaliate immediately. Hezbollah has dispatched hundreds and perhaps thousands of its fighters to Syria in support of President Bashar al-Assad’s regime, leaving the group in no position to also fight a war with Israel.

But the airstrike, Israel’s first against the Iranian-backed Hezbollah in Lebanon since the two sides fought a devastating but inconclusive war in 2006, underscored the danger that the Syrian war could escalate into a regionwide conflict.

Israel is thought to have carried out at least five strikes against targets inside Syria. According to U.S. officials, the attacks have been aimed at preventing transfers of missiles to Hezbollah. Israel has not confirmed or denied any of the strikes, but it has repeatedly vowed to prevent the group from acquiring sophisticated missiles.

“Israel has to act in order to prevent the transfer of game-changing weapons,” said retired Maj. Gen. Eyal Ben-Reuven, speaking from northern Israel. “Although I can’t confirm what happened . . . it is very clear that we are trying to prevent this.”

“We will do all that is necessary to defend our citizens,” Israeli Prime Minister Benjamin Netanyahu responded when asked about the attack Tuesday.

The Hezbollah statement disputed Lebanese news media reports that the strike had targeted a missile storage center and killed at least four Hezbollah fighters. The site “was only partially damaged,” the group said.

But according to a Lebanese intelligence official, the strike did target a shipment of missiles that had crossed the border from Syria. The official, who spoke on the condition of anonymity because of the sensitivity of the subject, said that he did not know exactly what had been hit in the raid but that more attacks are likely because other missile transfers have already been made.

The secretive Hezbollah movement is thought to maintain a military training ground and other facilities in the area to support its forces operating in Syria. Attacks on the bases “could paralyze Hezbollah movements and communication lines with Syria,” the intelligence official said.

Ben-Reuven predicted that Hezbollah would not respond because of its preoccupation in Syria. “However, our logic in the Middle East is that anything can happen, and, therefore, we have to prepare ourselves for all kinds of scenarios,” he said.

Hezbollah may also seek to retaliate with attacks on Israeli targets elsewhere in the world, such as a 2012 suicide bus bombing in Bulgaria. Authorities there accused Hezbollah operatives of carrying out the attack, in which five Israelis and the Bulgarian bus driver were killed. Hezbollah denied responsibility.

Ruth Eglash in Jerusalem and Ahmed Ramadan in Beirut contributed to this report.