**This post will be revised as ABC News coverage plans are updated**

ABC News to Air Special Expanded One-Hour Edition of "World News with Diane Sawyer" on Monday Evening

Terry Moran to Anchor "Nightline" From Boston Monday Night

George Stephanopoulos and Josh Elliott to Report From Boston for "Good Morning America" Tuesday Morning

Diane Sawyer and George Stephanopoulos anchored an ABC News special report to the ABC Television Network. ABC News producer Kendall Heath, who was on the scene at the marathon, is talking to Sawyer and Stephanopoulos on the phone. In addition, Senior Justice Correspondent Pierre Thomas and Chief GlobalAffairs Correspondent Martha Raddatz are reporting on security measures and reaction to the incident by Homeland Security; Chief White House Correspondent Jonathan Karl is reporting on the reaction from the Administration. Sawyer and Stephanopoulos also are talking to eyewitnesses on the phone who are describing the scene for viewers. ABC News is live streaming the network'sspecial report across its digital and mobile platforms here: http://abcnews.go.com/LIVE

Update (5:00 p.m.): ABC's Linsey Davis is currently reporting from Boston for all ABC News broadcasts and platforms. Chief Investigative Correspondent Brian Ross is en route to Boston to cover the ongoing investigation.

ABC News is covering the breaking news across all broadcasts and platforms:

"World News with Diane Sawyer" will expand to one-hour on Monday night. Diane Sawyer will anchor a special edition of the newscast from ABC News Headquarters with reports from the team that has been covering the developing story all afternoon.

will expand to on Monday night. Diane Sawyer will anchor a special edition of the newscast from ABC News Headquarters with reports from the team that has been covering the developing story all afternoon. " Nightline " will dedicate its broadcast to the developing story on Monday evening. Terry Moran will anchor "Nightline" from Boston.

will dedicate its broadcast to the developing story on Monday evening. will anchor "Nightline" from Boston. " Good Morning America " will have special coverage on Tuesday morning with George Stephanopoulos and Josh Elliott reporting from Boston.

" will have special coverage on Tuesday morning with and reporting from Boston. ABCNews.com has live updates here: http://abcn.ws/11ikV1p. ABC News and Yahoo! News will live-stream "AFTER: The Boston Marathon Bombings" Tuesday morning at 10:00 a.m., ET. Watch here: http://abcnews.go.com/live

has live updates here: http://abcn.ws/11ikV1p. ABC News and will live-stream "AFTER: The Boston Marathon Bombings" Tuesday morning at 10:00 a.m., ET. Watch here: http://abcnews.go.com/live ABC News Radio Correspondent Aaron Katersky will be reporting from Boston.

Correspondent will be reporting from Boston. ABC NewsOne Correspondents Marci Gonzalez and Tahman Bradley will report from Boston for more than 200 ABC affiliates, stations and clients.

Watch the ABC News Special Reports that began airing shortly after 3 p.m., ET:

Boston Marathon Explosion Was 'Horrifying': Hayden Cardy describes the scene in Boston following two explosions -

Boston Police Department reports at least two deaths after explosion at finish line -