Behind the metal door and up a narrow, blackened stairwell, fear hung in the air along with the smell of smoke. No one wanted to talk. A young woman scrubbing clothes in a plastic basin mutely shook her head. A man sweeping the floor with a toddler clinging to his legs said one word: "No." Another, bringing bags of food from the nearby market, brushed past without making eye contact.

As for the 10 Eritreans who had been trapped in a ground-floor apartment when the blaze began at 3am, they had gone. Four were in hospital suffering from burns and smoke inhalation; the rest had fled.

The overnight firebombing of a downtown Jerusalem building which houses refugees from sub-Saharan Africa was the latest in a string of attacks set against the backdrop of rising anti-migrant sentiment in Israel, fuelled by inflammatory comments by prominent politicians. Often described as infiltrators by ministers, the media, the army and government officials, migrants have also had labels such as "cancer", "garbage", "plague" and "rapists" applied to them by Israeli politicians.

The arsonists who struck the Jerusalem apartment, located in a religious neighbourhood of the city, scrawled "get out of our neighbourhood" on its outside wall. Police spokesman Micky Rosenfeld said: "This was a targeted attack which we believe was racially motivated." The foreign ministry condemned the "heinous crime".

But on the street outside the building, the official response had little resonance with a man who arrived in Israel from Eritrea 14 years ago but was too scared to give his name. "People look at you, they curse you. They say, 'Go back to your country.' We are very afraid," he said.

Tensions were inevitable, according to Moshe Cohen, the owner of a nearby jeweller's shop. "They drink, they fight among themselves, they play African music on shabbat [the Jewish sabbath] when people want to pray. What started in Tel Aviv happens here now."

He was referring to a series of firebombings of apartments and a nursery over the past month in southern Tel Aviv, an area in which African migrants are concentrated. Shops run by or serving migrants were smashed up and looted in a violent demonstration last month in which Africans were attacked. Many Israelis were shocked at the display of aggressive racism in their most liberal city.

Political leaders did not allow the violence to temper their verbal onslaught against the migrants. Prime minister Binyamin Netanyahu said Israel's national identity was at risk from the flood of "illegal infiltrators". Interior minister Eli Yishai suggested that Aids-infected migrants were raping Israeli women, and all, "without exception", should be locked up pending deportation. They do not believe "this country belongs to us, to the white man", he said in an interview.

And, while touring the fence that Israel is building along its border with Egypt to deter migrants, MP Aryeh Eldad said: "Anyone that penetrates Israel's border should be shot – a Swedish tourist, Sudanese from Eritrea, Eritreans from Sudan, Asians from Sinai. Whoever touches Israel's border – shot." He later conceded that such a policy may not be feasible "because bleeding hearts groups will immediately begin to shriek and turn to the courts".

According to the immigration authority, there are 62,000 migrants in Israel, where the population is 7.8m. Over 2,000 migrants entered Israel via Egypt last month, compared with 637 last May. The construction of the 150-mile (240km) southern border fence, due to be completed later this year, is thought to be increasing in the short term the numbers attempting to cross into Israel .

Nearly all are given temporary permits to stay in Israel which must be renewed every three or four months and specifically exclude permission to work. Many end up being employed on a casual basis for a pittance, living in overcrowded, rundown apartments and confined to the fringes of society. In desperation, some turn to petty crime.

On Sunday, a law came into effect allowing the Israeli authorities to jail migrants for up to three years. People helping or sheltering migrants could face prison sentences of between five and 15 years.

Netanyahu also ordered ministers to accelerate efforts to deport 25,000 migrants from countries with which Israel has diplomatic relations, principally South Sudan, Ivory Coast, Ghana and Ethiopia.

He conceded it was not possible to deport around 35,000 migrants from Eritrea, Sudan and Somalia. Eritreans and Sudanese make up more than 90% of those who have illegally crossed the Israel-Egypt border in recent months.

One out of 4,603 applicants was granted asylum status last year.

Although some commentators and community activists have said that Israel, a state founded by and for refugees from persecution, should be sympathetic and welcoming to those fleeing violence and oppression, the prevailing mood is one of intolerance.

"This phenomenon is getting bigger and bigger," said Poriya Gets of the Hotline for Migrant Workers, based in Tel Aviv. It was being stoked by politicians and rightwing organisations, she added. "We now see hotspots of tension between refugees and local people in many towns."

Her organisation had also been targeted. "We've had phone calls, people cursing and saying ugly things, like, 'We hope you will be raped and we are coming to burn you.' The politicians must take responsibility. They are trying to make the fire bigger."