JERUSALEM — Israel began work Monday on a border fence along its frontier with Egypt that is meant to keep out Islamic militants and African migrants, the Defense Ministry said.

Bulldozers were dispatched to three points along the 150-mile (250-kilometer) boundary and Israeli TV showed them clearing patches of land and digging trenches near Egyptian border posts.

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Israel approved the fence earlier this year in a bid to keep out militants believed to be operating in Egypt's Sinai desert and migrants from Africa.

The project is estimated to cost $370 million, the ministry said, and will take up to two years to complete.

The fence is expected to cover at least 87 miles (140 kilometers) of the boundary and will be backed up by an electronic barrier. Senior Defense Ministry official Udi Shani told Israeli Channel 10 TV the fence was part of a greater strategy to reduce the number of illegal migrants in Israel that would include the building of a giant holding room and the return of migrants to their home countries.

Israel began discussing the fence after its withdrawal from the Gaza Strip in 2005, fearing militants would attack Israel through Egypt.

The fence has been given added urgency in recent years because of the massive influx of African migrants into Israel. Human rights workers estimate some 17,000 to 19,000 people have poured into Israel through the southern border since 2005 in search of a better life in Israel's relatively affluent, Western-style society. Most come from Eritrea, Sudan and other impoverished African countries.