(New throughout, adds comment by U.S. official)

WASHINGTON, April 29 (Reuters) - The United States said on Friday it was in discussions with Russia about trying to renew the cessation of hostilities in Syria following the deadly bombing this week of a hospital in Aleppo.

"Our hope is by refreshing this agreement ... we can build momentum again toward a broadly observed cessation of hostilities," White House spokesman Josh Earnest told a briefing.

Efforts to push for an immediate halt to fighting came amid a surge in fighting between Syrian government forces, backed by Moscow, and opposition groups supported by a U.S.-led coalition.

A senior State Department official said the United States was seeking to halt fighting in Latakia and eastern Ghouta near Damascus as a test case to trying to revive the cessation of hostilities throughout the country, including in Aleppo.

"This is all something of a test, obviously, that we want to work, and we are working hard to make sure that it works, so hopefully in the end it will be open-ended," the official told a conference call, referring to the planned halt to fighting in Latakia and eastern Ghouta.

The official said the United States was also trying to stop the fighting elsewhere in the country, particularly in Aleppo, which has been the scene of the worst recent violence.

"We are working on all of the areas, it's not just about Latakia and eastern Ghouta, but also about Aleppo and other areas where we see problems or potential problems that we're trying to get this cessation of hostilities back on track," the official added.

U.S. Secretary of State John Kerry and his Russian counterpart, Sergei Lavrov, discussed ways to strengthen the ceasefire during a phone conversation on Friday, U.S. and Russian officials said.

There appeared to be some confusion over what had been agreed on Latakia and eastern Ghouta suburb and by whom. Syria's army said a new "regime of calm" would begin from 1 a.m. on Saturday and last one day in Ghouta and three days in the northern countryside of the coastal province of Latakia.

But a Syrian army statement said the "regime of calm" would not include a halt to combat in Aleppo, where the worst fighting has taken place.

Later, State Department spokesman Mark Toner told a briefing the plan was to first enforce ceasefires in Latakia and eastern Ghouta before expanding it to other areas.

(Reporting Lesley Wroughton, Arshad Mohammed, Susan Heavey and Doina Chiacu; Editing by David Gregorio) ((lesley.wroughton@thomsonreuters.com; +1 202 898-8393; Reuters Messaging: lesley.wroughton.thomsonreuters.com@reuters.net))

Keywords: MIDEAST CRISIS/SYRIA WHITE HOUSE