Three Syrian tanks entered the demilitarised zone in the Golan Heights between Israel and Syria, an Israeli military spokeswoman said.
"The Israeli Defense Forces have filed a complaint with the UN (peacekeeping) force in the area," the spokeswoman said. She had no further information on what the tanks were doing.
Israeli media said the tanks were involved in fighting in the Syrian village of Beer Ajam against rebels trying to overthrow President Bashar al-Assad.
Israel is technically at war with Syria, but it has generally taken a cautious line on the uprising in its Arab neighbour.
Errant Syrian mortars bombs landed in Israel in September, spurring Israel to lodge a similar complaint with the United Nations observer force that monitors a long-standing, de-facto truce between the two countries.
Israel captured the Golan Heights, a strategic plateau, from Syria during a 1967 Middle East war. It later annexed it in 1981 in a move not recognised internationally.
In Washington, the White House had no immediate comment.
Earlier Syrian activists said rebels and government troops were fighting for control of a key airbase in the country's north.
The Syrian Observatory for Human Rights said the rebels had launched a dawn offensive to take Taftanaz air base, a day before a crucial opposition conference in Qatar.
Taftanaz lies near the highway between the capital Damascus and the northern city of Aleppo, a major front in the civil war.
Activist videos posted online claim to show the attack on Taftanaz.
A rebel vehicle fires rockets and smoke rises over buildings and what appears to be an airstrip. The videos appear genuine and are consistent with other Associated Press reporting in the area.
Activists say more than 36,000 people have been killed in Syria since the uprising began in March 2011.
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