JERUSALEM (AP) — A roadside bomb hit an Israeli patrol near the frontier with the Golan Heights on Tuesday, the army said, wounding four soldiers in the most serious violence to strike the area since the Syrian conflict began three years ago. Israel said it responded with artillery strikes on Syrian army targets.

Lt. Col. Peter Lerner, a military spokesman, said the patrol noticed "suspicious movement" along the frontier, and when they went to investigate, the blast went off. "Clearly this is a grave result and we will be following it," he said. The army later added that one of the soldiers was seriously wounded.

It was the latest in a series of incidents in the volatile area. Last week, a roadside bomb went off near a military patrol along the Lebanese border, causing no injuries. Earlier this month, the army said it killed two militants affiliated with Hezbollah, the Lebanese militant group fighting alongside Syrian government troops, who were trying to plant a bomb along the frontier.

Although Lerner said it was too early to blame any group for Tuesday's attack, Israel has been on high alert for an attack by Hezbollah since an Israeli airstrike last month targeted a suspected weapons convoy of the group in southern Lebanon. Hezbollah vowed to avenge the strike, though Israel has never confirmed carrying it out.

Israel has said it will not allow sophisticated weapons to flow from Syria to the Iranian-supported Hezbollah, an ally of Syrian President Bashar Assad and a heavily armed foe of the Jewish state.

Lerner said Israel targeted Syrian positions Tuesday because it holds Syria responsible for all attacks emanating from its territory.

"We view the Syrian army as responsible for the incident," he said. "I can't confirm that it was Hezbollah behind this, but it wouldn't be the first time. Last week there was an incident of explosive devices in the vicinity and we do see increased involvement of Hezbollah in Syria."

Israel and Hezbollah are bitter enemies and fought an intense monthlong war in 2006.

Israel captured the Golan Heights from Syria in the 1967 Middle East war and later annexed the strategic area in a move that was not internationally recognized. Israeli forces have come under fire on several occasions since a rebellion against Syrian President Bashar Assad broke out in 2011. Israel has been carefully monitoring the Syrian war since the fighting began.

While relations are hostile, the ruling Assad family has kept the border area with Israel quiet for most of the past 40 years. Israel is concerned that Assad's ouster could push the country into the hands of militant Islamic extremists or sectarian warfare, destabilizing the region.

Israeli Prime Minister Benjamin Netanyahu said he will act against such attacks.

"The frontier with Syria has been filling up recently with Jihadi elements and Hezbollah and this presents a new challenge to the state of Israel," he told Army Radio. "In recent years we have succeeded in preserving the quiet before the civil war in Syria, and we will act with forcefulness to preserve Israel's security," he said.

The Syrian fighting, mostly errant fire, sometimes spills over into Israeli border communities, damaging property and crops, spreading panic and sparking fires. Israel occasionally retaliates.

Despite the animosity, dozens of wounded Syrians have reached the frontier, and Israeli soldiers have brought them into the country for treatment at Israeli hospitals.

U.N. spokesman Stephane Dujarric said the U.N. peacekeeping force monitoring the disengagement of Israeli and Syrian forces on the Golan Heights, UNDOF, has been in touch with the Israeli Defense Force and the senior Syrian Arab delegate.

"The IDF has confirmed to UNDOF that it observed an individual crossing the cease-fire line and that an IDF patrol was sent to the location. The IDF soldiers got out of their vehicle and crossed the technical fence when an improvised explosive device exploded, resulting in injuries," Dujarric said.

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Edith M. Lederer contributed reporting.