Over 650 armed Hamas terrorists have been killed since the Cast Lead operation in Gaza began more than two weeks ago, senior IDF officials said Monday. Four hundred are known to have been working with Hamas, while at least another 250 of those killed are believed to have been fighting for the terrorist group, they explained.

Many of the dead were killed in clashes with IDF ground troops. Fifty were killed on Monday, officers estimated.

Approximately 900 residents of Gaza have been killed in the operation. Of the roughly 250 killed who were not members of Hamas, some were members of other terror groups, while others were killed by stray fire, many after leaving their homes despite the fighting.

The IDF continued to hit Gaza targets on Monday. Israel Air Force planes hit more than 25 targets, including 10 groups of Hamas terrorists, two of them in moving vehicles. Also hit were mortar shell launchers and launch pads.

Soldiers fighting in Gaza have continued to discover tunnels and weapons caches. On Monday, soldiers discovered anti-aircraft missiles and mortar shells, along with guns and smaller bombs. A tunnel was found underneath a house in northern Gaza.

Despite the heavy casualties suffered by Gaza terrorists, groups continued to fire rockets at Israeli cities on Monday, hitting Ashkelon and Be'er Sheva along with several smaller towns. The frequency of rocket fire has decreased, however, with terrorists firing just over 20 rockets a day compared to over 70 a day in the first week of the operation.