JERUSALEM, Sept 5 (Reuters) - Israel ruled out entry on Wednesday for 20 Africans who have camped on its desert border with Egypt for almost a week, part of a crackdown on migrants who walk across the porous frontier.

About 60,000 Africans have come into Israel through the Egyptian Sinai in recent years. Israel says the vast majority are illegal job seekers, disputing arguments by humanitarian agencies that they should be considered for asylum.

The 20 Africans arrived at the guarded border fence on Thursday, according to Israeli media, which said they were from Eritrea and included at least one woman and child.

"This group must not enter," Interior Minister Eli Yishai said in a television interview. "We are acting in accordance with the law. They came here knowing they would not get in."

"It is very difficult to see this, but if we let them in others will follow. The fence is there to protect the borders of the state of Israel," he said.

The Israeli military said it was providing the migrants with water. Troops turned back human rights activists who attempted to reach the scene with food, but the activists said they had received assurances from the army that the food would be given to the migrants.

The fence along the 260 km (160 mile)-long frontier with the Egyptian Sinai, which is still being built and is due to completed by the end of the year, is among measures introduced by Israel to bar African migrants.

Israeli ministers say the influx of African migrants is a threat to public order and could change the demographic character of the Jewish state of 7.8 million. (Writing by Ori Lewis; Editing by Pravin Char)