Ukraine ceasefire 'mostly holding': US

A Ukrainian serviceman bends down as he hears shooting in the small eastern city of Debaltseve, on September 9, 2014 (AFP Photo/Anatolii Stepanov)

Washington (AFP) - The United States said Tuesday the ceasefire in Ukraine was "mostly holding," adding that conditions on the ground would be a factor as it mulls imposing additional sanctions against Russia in "the next few days."

State Department spokeswoman Marie Harf said the ceasefire agreed on Friday between Kiev and pro-Russian separatists has been successful, although have been reports of mortar attacks and sporadic gunfire in areas such as the Donetsk airport and Lougansk.

"Obviously it's something we are continuing to monitor," Harf said.

The United States was "ready to impose more" sanctions against Russia, but "we are going to make decisions based on what is happening on the ground in the next few days," she added.

Harf said the United States was working closely with the European Union to "both deepen and broaden our sanctions across Russian financial energy and defense sectors."

Questioned about the preliminary report into the shooting down of the Malaysia Airlines flight MH17 over Ukraine in July, Harf said Russia still had "many questions" to answer.

"About the possible involvement of its equipment, about the separatists, about their involvement in the event that led to the crash of this airplane," Harf said.

"We, and not just us, but more importantly the families of the victims, deserve answers."