Foreign Minister Julie Bishop has said "all trust has broken down" between the United States and Russia over Syria, and described the bombing of the city of Aleppo by regime forces as an "unprecedented" atrocity.

Her remarks, reflecting the scale of the destruction and the backslide in international efforts to rein in the violence, followed reports of a regime air strike on a hospital in eastern Aleppo.

Speaking on the ABC's Insiders program, Ms Bishop also said a Lockerbie-style international tribunal – referring to the 1988 Libyan bombing of an airliner over Scotland – could be used to bring to justice those behind the downing of flight MH17.

On Syria, Ms Bishop painted perhaps the bleakest picture yet of the intractable conflict. She said "all options" had to be on the table, including an arms embargo in which the US and Russia withdrew military support for the rebels and regime respectively.