Republicans are wading into the special election to replace the late Rep. John Murtha (D-Pa.), according to a source.

The source tells The Hill that the National Republican Congressional Committee (NRCC) has placed an ad buy in the district, signaling it tends to go after the swing district in the May 18 primary. The committee has not confirmed the buy.

There had been some uncertainty as to whether the GOP would seriously go after the seat, given the built-in advantage the Democrats have by holding the special election on the same day as the primary. Most of the top races that day are being waged on the Democratic side.

The Democratic nominee is Murtha's former district director, Mark Critz. Republicans are running businessman Tim Burns.

There is no indication as to the size of the NRCC buy.