The enlargement of the EU to include former Warsaw Pact countries such as Romania has created a "gateway for organised crime", the Ukip leader, Nigel Farage, has said.

As more damaging details emerged about the views of Ukip candidates, Farage admitted his party had made mistakes in its selection of candidates. He said Ukip would attempt to change perceptions this week when it published its election addresses for the local elections, featuring black and minority ethnic candidates.

Farage said the presence of Romanians in Britain posed a threat, warning of an explosion in organised crime. Expanding on his answer in a Guardian interview last month, when he spoke of how discomfiting it would be to live next door to Romanians, Farage told the Andrew Marr Show on BBC1: "We have opened up the doors to countries that have not recovered from communism and I'm afraid it has become a gateway for organised crime. Everybody knows that. No one dares say it."

The remarks appeared to be aimed at Romania and Bulgaria, two former Warsaw Pact countries that joined the EU in 2007. A further eight former Warsaw Pact countries, led by Poland, joined the EU in 2004. Farage is concerned about immigration from the so-called A8, but his remarks appeared to be aimed at Romania and Bulgaria because they are less developed economically.

Farage insisted his party was not racist after the Sunday Times reported that a candidate in Stockport had resigned after calling Islam "evil". The Ukip leader said: "We have made mistakes. But these people are not representative of Ukip at all. Not only am I adamant that we are a non-racist party, this week we are going to fight back against it. You will see our election address for the local elections this year and you will see a lot of black ethnic minority candidates who are proudly standing for Ukip. I am going to approach this differently in future."