Israeli forces fought with members of the Islamic group Hezbollah for hours Monday along the Israel-Lebanon border, Israeli military officials said, in the most sustained combat on the northern frontier in five months.

The officials said four Hezbollah gunmen were killed in the fighting, which included Israeli airstrikes on targets in southern Lebanon, while eight Israeli soldiers and three civilians were wounded by rifle and mortar fire.

Israeli forces in the region have been on alert for weeks based on reports that Hezbollah, the Shiite Muslim militia funded in part by Iran and assisted by Syria, planned to kidnap soldiers inside a disputed area known as Shebaa Farms. Israeli forces took the border strip from Syria in the 1967 Middle East war, although Hezbollah and the Lebanese government claim the land as part of Lebanon. The United Nations says the Israeli-occupied area is Syrian.

"This was definitely an operation planned some time ago," said Capt. Yael Hartmann, an Israel Defense Forces spokesman. "These operations are usually launched when the timing is right for them."

Hezbollah waged an intensive guerrilla war during Israel's 18-year presence in Lebanon, which ended with a unilateral Israeli withdrawal in May 2000. Members of the group, which operates a political party and social services network in Lebanon, often stage hit-and-run attacks along the fortified border to highlight the dispute over Shebaa Farms.

The northern border had been quiet since June, when Hezbollah fired mortar shells into Shebaa Farms, killing one Israeli soldier.

About 3 p.m. Monday, Israeli military officials said, Hezbollah forces began shelling Israeli positions in Shebaa Farms, an area of about 100 square miles including militarized buffer zones around it.

At the same time, Israeli military officials said, a group of Hezbollah fighters crossed into the town of Ghajar along the border between Israel and Shebaa Farms. Hezbollah gunmen fired on Israeli military positions, including a sentry tank that was damaged by an antitank round.

The mortar and rocket fire, which also struck a house in the Israeli city of Metulla, appeared designed to distract Israeli soldiers during the suspected kidnapping operation in Ghajar. The military ordered Israeli residents of the area into basements and bomb shelters for several hours.

Israeli warplanes hit a Hezbollah command post in southern Lebanon and bombed several roads used by Hezbollah fighters to transport supplies, Israeli officials said. The shelling continued into the evening.