Texas Governor Rick Perry has asked Mexico's president to call him in the next 48 hours to discuss the search efforts for the body of an American reportedly shot dead on a border lake.
Mr Perry said he hopes the body has been retrieved by the time he gets the call from Felipe Calderon, adding: "If not, we're not looking hard enough."
Tiffany Hartley says her husband, David, was shot by Mexican pirates on Falcon Lake last week as they were returning to the United States on jet-skis.
Falcon Lake is a dammed section of the Rio Grande that has been plagued by pirates who rob boaters and fisherman who wander into Mexican waters, but Mr Hartley's death would be the first killing on the lake.
The Mexican Foreign Relations Ministry responded with a statement that noted Mexico's "condemnation of any act that endangers the lives of innocent citizens", saying the country "is committed to the investigation of those acts."
The statement said Mexico has "from the first moment" been in contact with the US to coordinate the search and recovery of Mr Hartley's body, and noted that Mexican authorities have "stepped up their actions with the support of specialized personnel, boats and helicopters".
Tiffany Hartley has said her husband was shot in the head by three men chasing them in speedboats and that he fell off his jet-ski and into the lake. His body has not been recovered.
Mrs Hartley and several relatives took boats out onto the water of the US side on Wednesday to lay a wreath for him, and she told a news conference later that she wanted to honour her husband.
"It was very emotional because I know he's out there and we just all want him back so we can give him the proper goodbye," she said.
Mr Perry said Mexico needs to use every resource available to find the body and have it returned to US soil.