The nooses appeared on lampposts with posters signed by far-right group Forza Nuova in the city of Pescara where the minister for integration was visiting for a conference on immigration and citizenship.
"Immigration, the noose of the people!" read one of the slogans on the posters. Another said: "Everyone should live in their own country".
Kyenge, who is of Congolese origin, has called for a reform of Italian law to make it easier for children born to immigrant parents to acquire citizenship.
Prime Minister Enrico Letta called for an end to the insults against Kyenge, saying this was a "shameful chapter" for Italy and could lead to a "major clash".
Ever since being named to the cabinet in April, Kyenge has faced a barrage of abuse – particularly from members of the anti-immigration Northern League party.
Northern League MEP Mario Borghezio said her nomination was "bloody stupid" and that she had "a face like a housewife", while one local party activist said the minister should be raped in a vicious Facebook rant about crimes committed by immigrants.
Northern League senator Roberto Calderoli, who has courted controversy for years with a series of racist, sexist and Islamophobic jibes, on Saturday said: "When I see pictures of Kyenge, I cannot help thinking of similarities with an orangutan".
In an interview with La Repubblica daily out on Monday, Calderoli then claimed that he had animalistic comparisons for all the ministers, including ones who looked like a frog, a peacock and a St Bernard's dog.
Letta on Monday said Calderoli's remarks were "unacceptable" and called on Northern League leader Roberto Maroni to put an end to the attacks by his party members "as quickly as possible".
Calderoli is deputy speaker of the Senate and there have been calls for his resignation from centre-left lawmakers and anti-racism campaigners.