The office of Serbian President Boris Tadic issued a statement saying that the two officials stated that cooperation with the Hague tribunal would fully open Serbia's European prospects.
Serbian Prime Minister Vojislav Kostunica said during talks with Williamson that the action plan had only one goal - to locate, arrest and transfer to the tribunal Ratko Mladic and other indictees.
Ambassador Williamson underlined the importance of maintaining and developing continued regional cooperation in discovering and prosecuting war crimes, the Serbian government said in a statement.
PM Kostunica paid special attention to the issue of failure to punish war crimes committed against Serbs, the statement said.
The US ambassador and Serbian War Crimes Prosecutor Vladimir Vukcevic discussed a draft agreement on cooperation and prosecution of the perpetrators of war crimes, crimes against humanity and genocide, which Zagreb and Belgrade are expected to sign soon.