Prime Minister Benjamin Netanyahu has promised to step up efforts to deter, detain and deport illegal migrants to Israel, as tensions mount over an influx of asylum seekers from Africa. His pledge came a day before an early morning fire, apparently set by arsonists, ravaged an apartment occupied by about 10 Eritrean migrants on Monday. Four people were injured.

Though there have been a number of firebomb attacks against migrants in south Tel Aviv in recent weeks, the fire was the first attack on migrants in Jerusalem, the police said.

Dozens of foreigners, including families with children, lived in the building where the fire broke out, on Jaffa Road, one of the city’s central arteries. Four residents were taken to a hospital with burns to the hands and smoke inhalation. Graffiti sprayed on a stone wall by the entrance of the building read: “Get out of the neighborhood.”

Mr. Netanyahu has condemned violence against illegal migrants, who are known here by the Hebrew word for infiltrators. But he has also expressed a policy of zero tolerance for the flow of Africans crossing surreptitiously into Israel from the Egyptian Sinai.

An estimated 60,000 Africans have entered Israel over the last few years. While Israel acknowledges that some may be genuine refugees from war-torn countries, it has no system for registering them as refugees; most of the border crossers, Israel says, are economic migrants seeking work in Israel.

In a closed meeting with Likud Party cabinet ministers on Sunday, Mr. Netanyahu pledged to complete a 150-mile, 16-foot-tall steel fence now being erected in the desert along the Israeli-Egyptian border; to speed up construction of a detention facility able to hold up to 10,000 illegal immigrants; and to step up efforts to deport foreigners who may be legally repatriated to their home countries according to international conventions.

Mr. Netanyahu intends to start repatriating several thousand South Sudanese people in Israel, but is awaiting approval from the Israeli Supreme Court, according to an official who was in the meeting.

Under a new Israeli law, illegal entrants can be held in detention for up to three years, a provision that the official said was meant in part to deter economic migrants.

“It is important to understand that international law makes deportation very difficult,” Mr. Netanyahu noted last week in a speech in Tel Aviv. Although “it is not a problem that can be solved overnight,” he said, “we can deport them, and we will.”

“Just as we solved other problems,” he said, “we will solve this problem methodically and responsibly, in accordance with international agreements.”

Still, most African migrants in Israel are from Sudan or Eritrea. Since sending them back could put them at mortal risk, they are afforded blanket protection in Israel, in line with international conventions.

The issue has become an explosive one in Israel. Many African migrants have settled in poor areas of south Tel Aviv and in the southern border town of Eilat, and have met increasing resentment.

Residents of south Tel Aviv complain of rising crime in migrant areas, and have staged noisy demonstrations, egged on by right-wing politicians and activists. At a demonstration in the Shapira Quarter last week, rightists handed out leaflets offering self-defense courses, and protesters chanted, “The people want the Sudanese deported,” holding placards with slogans like, “This is not racism, this is survival.”

Some stores run by African migrants were damaged and looted last month.

“It was better in Sudan,” said Ibrahim Abdullah, 25, an asylum seeker who was idling on the grass in a south Tel Aviv park last week. Mr. Abdullah said that he worked now and again in building, but that he had no money and relied on handouts for food.

Israel’s interior minister, Eli Yishai of the ultra-Orthodox Shas Party, was quoted on Friday as saying that “the infiltrators, along with the Palestinians, will quickly bring us to the end of the Zionist dream.” Noting that Israel had its own health and welfare issues, he said, “We don’t need to import more problems from Africa.”

“Most of those people arriving here are Muslims who think the country doesn’t belong to us, the white man,” Mr. Yishai said in an interview with the newspaper Maariv.

Even so, there has been emotional debate here about the obligations of a country like Israel, largely founded by refugees. While opponents of the African influx say they worry about Israel’s future as a state with a Jewish majority, other Israelis have volunteered to help the asylum seekers and say that Israel, of all places, should show compassion toward those fleeing hardship.