NEW ORLEANS (Reuters)—A federal judge on Monday denied BP P.L.C. access to 21 emails and other documents sent among White House and other U.S. officials related to the 2010 Gulf of Mexico oil spill, citing the government's need to keep them confidential.

U.S. Magistrate Judge Sally Shushan in New Orleans said the federal interest in preserving secrecy, together with the public interest in ensuring an effective response to the next disaster, outweighed BP's need for the documents to defend itself in litigation by the government over the spill.

"This conclusion is not altered by the role of the U.S. in the response to the spill as well as its role as a plaintiff against BP," Judge Shushan added. The judge said she reviewed the documents in private before ruling.

Scott Dean, a BP spokesman, declined to comment.

The April 20, 2010, explosion of the Deepwater Horizon killed 11 people and triggered several hundred lawsuits against BP and its drilling partners, including rig owner Transocean Ltd. and cementing service provider Halliburton Co.

U.S. District Judge Carl Barbier in New Orleans has scheduled a trial Jan. 14, 2013, to allocate blame. BP reached a $7.8 billion settlement in March with more than 125,000 local individuals and businesses, which awaits court approval.

Sarah Himmelhoch, a U.S. Department of Justice lawyer, had argued in a June 5 letter that letting BP see the 21 documents would signal that "there is no protected space for government workers and decision makers in the midst of a national emergency. This could chill communications during the next disaster, harming the public by impeding the speed and quality of the government response."

But in a June 8 letter, BP lawyer Robert Gasaway countered that it would be "fundamentally unfair" to keep the documents private. He said the documents were "almost certainly" relevant to BP's defense against expected U.S. civil claims under the Clean Water Act, because they addressed how much oil was being spilled and BP's role in capping the Macondo well.

Among the senders and recipients of the 21 documents were Energy Secretary Steven Chu; Interior Secretary Kenneth Salazar; and Carol Browner, former director of the White House Office of Energy and Climate Change Policy. The Department of Energy has said it has turned over more than 719,000 documents to BP.

On Friday, the Financial Times said BP was "hoping" to reach a settlement of less than $15 billion with the U.S. government to resolve all criminal and civil claims, citing a person familiar with the discussions. Civil penalties under the Clean Water Act alone could reach $17.6 billion.