An FBI probe into alleged corruption in international soccer has intensified after investigators persuaded a key party to be a cooperating witness, US law enforcement sources said.

They said the witness is Daryan Warner, the son of former FIFA vice-president Jack Warner. The sources declined to further discuss the role of Daryan Warner, who could not be reached for comment.

They also would not say who might be charged, if anybody, or when. While the exact scope of the investigation is not clear, among the matters under scrutiny are two previously reported allegations involving Jack Warner, who is currently national security minister in his native Trinidad and Tobago.