JERUSALEM, Dec. 28 (UPI) -- The Israeli government Sunday approved a draft of more than 6,000 military reservists it says may be necessary for a ground offensive in Gaza, observers said.

The move came after a second day of Israeli air strikes pounded Gaza, targeting rocket launchers and military infrastructure controlled by the Palestinian militant group Hamas, in which up to 275 people have been reported killed. Israeli Defense Minister Ehud Barak told the Israeli Cabinet the reservists would be needed if the Gaza operation expands to include a ground operation, the Israeli Web site Ynetnews.com reported.

The Israeli army has begun mobilizing tanks and reinforcement infantry troops in the event a ground incursion is ordered, Ynet said. In an interview with Britain's SKY News, Barak did not say a ground assault was imminent, but did declare that ground forces would indeed enter the Gaza Strip if the move was deemed necessary by Jerusalem.

"This will be a long and difficult war which will be very painful," Prime Minister Ehud Olmert told the Cabinet, warning the Gaza operation may take longer than hoped for. "The expectation that we will be able to hit hundreds of terrorists a day cannot be realized."