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Natalie Bennett says she has "watched in horror" as migrants are blamed "for failures" in government policy.
The Australian-born Green Party leader told activists in a speech on immigration she rejected "those who try and divide us by our country of birth."
She accused politicians of attempting to "sound tough... to stave off the perceived threat from UKIP".
Conservatives want to tighten immigration controls. Labour has pledged prompt action on the issue.
UKIP wants to use an Australian-style points system to select migrants with skills and attributes needed in the UK, claiming annual net migration could be brought back to a "normal level" of about 50,000.
Divide and rule?
Ms Bennett made her speech at the Kurdish Community Centre in Haringey, north London, accompanied by Green MEP Jean Lambert, saying she was "taking a stand against those who seek to demonise" migrants like her.
She said the Greens would "never blame migrants for failures of government policy, or the greed and fraud of the bankers".
"Elections should be about discussion and disagreement - but on the topic of immigration we've seen the entire political establishment attempting to sound 'tough' in an attempt to stave off the perceived threat from UKIP," she said.
"As a migrant, and someone who loves this country for the tolerance it has shown those arriving on its shores, I've watched in horror as politicians line up to blame those not born here for failures in government policy.
"And as a migrant I utterly reject those who try and divide us by our country of birth.
"I may have been born on the other side of the world, but that doesn't mean that I don't love this country."
She said she was disappointed with Labour for not "standing up to Nigel Farage and his chums".
"Rather than showing real opposition, they have adopted a harsh rhetoric - proudly pledging their plans on banners and merchandise to 'control immigration'."
The Conservatives say they plan to "control immigration and build a system that puts the British people first".
"We will regain control of EU migration by reforming welfare rules, tackle criminality and abuse of free movement and cut immigration from outside the EU," a spokesman said.
Labour leader Ed Miliband said his party would set out a "credible" set of measures on immigration within 100 days of taking office.
He has pledged to recruit an extra 1,000 border staff, introduce full exit checks and stop serious criminals coming to the UK.
He also challenged David Cameron to match his pledges, accusing him of "abandoning the issue to UKIP".