Israel's new defence minister Moshe Yaalon has vowed an "immediate" answer to all Syrian gunfire onto the Israeli-occupied Golan Heights, saying the government in Damascus was responsible.
"Every violation of Israeli sovereignty and shooting from the Syrian side will immediately be answered by silencing the source of fire," he said in a statement.
His remarks were made shortly after Israeli troops on the strategic plateau fired an anti-tank missile at a Syrian army post after coming under fire for the second time in 12 hours, army radio said.
"We view with great seriousness the shooting last night and this morning from Syria at an IDF force on territory of the state of Israel," Yaalon said on Sunday.
"We see the Syrian regime as responsible for every breach of sovereignty. We shall not allow the Syrian army or any other body to violate Israeli sovereignty firing into our territory."
Earlier, a military spokesman said shots had been fired at troops in the southern Golan Heights.
'Nothing is clear there'
It was not immediately clear whether the shooting was from the Syrian army or from rebel forces in the area.
Late on Saturday, gunfire hit several military vehicles travelling in the same area, causing damage but no casualties, the army said. And earlier this month, a mortar round landed on the Israeli-controlled sector after nearly three months of quiet.
Last November, gunfire from Syria prompted troops to respond with artillery in the first instance of Israeli fire at the Syrian military since the 1973 war.
"Nothing is clear there," Amos Gilad, a top official in the defence ministry, told army radio. "The future is unclear, there are awful acts of murder, a danger of [the country] breaking apart, rising extremist terror, very strong involvement of Iran and Hezbollah," he said, referring to the Lebanese armed group and political party.
Earlier this month, Israel expressed concern that the UN peacekeeping force in the Golan Heights could pull out altogether after Syrian rebels snatched 21 of their troops in the ceasefire zone bordering Israel.
Since 1974, the UN has been monitoring the Syrian side of the armistice line with a force of 1,200 troops, although its number has recently dropped to 1,000.
Israel seized the Golan from Syria in the 1967 Six-Day War and annexed it in 1981, in a move never recognised by the international community. It is currently upgrading its security fence along its armistice line, with the work expected to be finished by the end of the year.
The United Nations estimates that violence across Syria has killed at least 70,000 people since the conflict erupted in March 2011.