September 12, 2011
Mr Richardson said Cuban Foreign Minister Bruno Rodriguez told him "it was not possible" to see Mr Gross, who is said to be in poor health.
The politician is in Cuba to secure Mr Gross' release. He has acted in the past as a diplomatic troubleshooter.
Mr Gross is serving 15 years for bringing internet equipment into Cuba.
The US has repeatedly demanded his release. His case has put a brief warming of US-Cuban relations, under President Barack Obama, on hold after decades of economic and political sanctions.
"I came here in good faith; I've had good conversations," said Mr Richardson at a news conference in Havana on Friday.
"This issue is not over, but I just wanted to send a signal that I'm staying here in Havana until I get to see Alan Gross."
He said he would be willing to stay for the Cuban baseball season, which opens in November.
"The legal process has ended and my hope is that the Cuban government now considers a humanitarian release," Mr Richardson said.
Mr Gross' family have asked for his release on humanitarian grounds, saying he is unwell and both his wife and daughter have cancer.
Mr Richardson arrived in Cuba on Wednesday, describing his visit as private. The Gross family said he was travelling at the invitation of the Cuban government.
He made a trip to Havana in August 2010, when he also raised Mr Gross' case, without winning any concessions.
Former US President Jimmy Carter also raised the matter during a visit to Cuba in March.
Alan Gross, 62, was arrested in December 2009 for distributing illegal communications equipment in Havana.
Last March he was convicted of crimes against the communist state.
He says he was just trying to help Cuba's small Jewish community get access to the internet.
Gross was in Cuba working as a contractor for the US Agency for International Development (USAID) on a secretive programme aimed at promoting democracy in Cuba.
Last month, Cuba's Supreme Court upheld his sentence, saying he was part of a programme aimed at "subverting" and "destabilising" the communist system.