Militants crossed from Egypt's turbulent Sinai desert into southern Israel on Monday and opened fire, killing an Israeli worker, defense officials said. Two assailants were shot dead in a gunbattle with Israeli troops responding to the ambush.

The Israeli was in a crew building a fence along the porous desert border.

No group claimed responsibility for the attack, which underscored the growing lawlessness in the Sinai desert since longtime Egyptian President Hosni Mubarak was toppled by a popular uprising last year.

Military spokeswoman Lt. Col Avital Leibovich said the assailants have not been identified but said defense officials suspect Palestinian militants in the Hamas-run Gaza Strip might have been involved. Southern Gaza borders Sinai, and infiltrators can exit Gaza through tunnels under the border.

Several hours after the attack, an Israeli airstrike killed two men on a motorcycle in the northern Gaza Strip near the Israeli border. The Islamic Jihad said the men were members on a "reconnaissance" mission and vowed revenge.