MANCHESTER, N.H. (AP) -- Law enforcement officials across the country widened their search for two missing New Hampshire children after their father pleaded innocent to killing them.

The search area includes Mercer County.

Manuel Gehring, 44, pleaded innocent Thursday in Hillsborough County Superior Court to two counts of first-degree murder.

His children, Sarah, 14, and Philip, 11, were last seen arguing with him at a July 4 fireworks display in Concord. Police believe he killed them after leaving the city and buried them the next day in the Midwest.

The FBI said Thursday it was now looking in Ohio and Pennsylvania based on new, unspecified information. Police are looking for the bodies, which may have been buried, in an area 10 miles north or south of Interstate 80.

Gehring may have stopped at Wal-Mart in Pine Township and bought something, according to a story this week in Allied News, Grove City.