US Democratic presidential nominee Barack Obama didn't know his aunt might be living illegally in the United States, his campaign said yesterday.

"Senator Obama has no knowledge of her status but obviously believes that any and all appropriate laws (should) be followed," campaign spokesman Bill Burton told reporters.

US media reported that a court refused four years ago to accept the asylum application of Zeituni Onyango, 56, the half-sister of Obama's Kenyan father.

However, she has continued to live in a public housing complex in South Boston.

Onyango's refusal to leave the country would be an administrative violation, not a criminal matter, according to the reports.

The US Immigration and Customs Enforcement spokeswoman Kelly Nantel declined to comment on the issue.

Democratic US Rep. John Conyers of Michigan asked Homeland Security Secretary Michael Chertoff to investigate whether someone leaked the information to the media in an effort to damage Obama.

The Department of Homeland Security had no immediate response to the letter.

The Obama campaign did not indicate whether Obama has been in touch with his aunt, whom he described in his book "Dreams from My Father."

It is not clear when Onyango arrived in the United States.

She once told media that she travels back and forth between the United States and Kenya.

Federal records indicate Onyango contributed at least 65 US dollars to Obama's campaign in July and September, in 5-dollar and25-dollar increments.

The Obama campaign said it has identified 265 dollars in contributions from Onyango, including those not yet reflected in federal filings, and plans to return the funds.