NABATIYEH, Lebanon — Israeli troops sealed off a Hezbollah stronghold in fierce fighting in south Lebanon and warplanes struck this market city today, killing six people. Guerrillas fired rockets at northern Israel, killing a girl, as the two-week-old crisis showed no signs of letting up, despite frantic diplomatic efforts.

Outlining the scope of the Israeli campaign for the first time, a senior army commander said Israel would only encircle Lebanese towns and villages near the border and did not plan a deeper push into the country.

"The intention is to deal with the Hezbollah infrastructure that is within reach," Col. Hemi Livni, who commands Israeli troops in the western sector of southern Lebanon, told Israel Army Radio, told Israel Army Radio. "That means in southern Lebanon, not going beyond that."

With the diplomatic threads for a solution still tangled, the violence looked likely to drag on with a new element after 14 days of bombardment: tough ground fighting as Israeli forces try to move village to village near the border, facing well-armed, determined Islamic militant guerrillas who have been digging in for years.

Hundreds of Americans and Russians, meanwhile, were feared stranded in the heart of Lebanon's war zone after a ship evacuating foreign nationals from the area left the port of Tyre on Monday evening.

A German official involved in the effort, Erik Rattat, said 300 Americans were trapped southeast of the town, and U.S. officials said they did not know if any of them were able to reach the boat before it left. Moscow said more than 100 Russians and citizens of other ex-Soviet republics also might be trapped.

U.S. officials also said the last scheduled evacuations of Americans from Lebanon would happen Wednesday.

At the front today, an Israeli military official said troops had surrounded Bint Jbail, a town that has symbolic importance to Hezbollah as one of the centers of resistance to the Israeli occupation from 1982 to 2000.

Israeli forces have seized some houses on the outskirts of the hilltop town since beginning the assault Monday, but do not yet control Bint Jbail, the official said.

Up to 200 Hezbollah guerrillas are believed to be defending the town, which lies about 2Z\x miles north of the border.