(Updates with detail, comment from Kerry, Australian foreign minister)
SYDNEY, Aug 12 (Reuters) - US Secretary of State John Kerry said on Tuesday he hoped the international community can find a way for Russia and Ukraine to work together to resolve political tension, but cautioned that the United States had not ruled out further sanctions.
Kerry was speaking as Russia said a convoy of 280 trucks carrying humanitarian aid set off for Ukraine on Tuesday, amid Western warnings against using help as a pretext for an invasion.
As Ukraine reported Russia has massed 45,000 troops on its border, NATO said there was a "high probability" that Russia could intervene militarily in the east of Ukraine, where its forces are closing in on pro-Russian separatists.
Kerry said he remained hopeful for a peaceful outcome to the crisis, which has prevented an international team from carrying out a full investigation into a downed Malaysian airliner, an incident the United States and other countries have blamed on pro-Russian separatists.
"Our hope is that in the next days and weeks, we can find a way for (Ukrainian) President Poroshenko and Ukraine to be able to work with the Russians to provide the humanitarian assistance necessary in the east, to facilitate the thoroughness of the investigation to begin to bring the separatists - to the degree that they are Ukrainian - into the political process and for those that are not Ukrainian, they need to leave the country," Kerry told reporters at a briefing in Sydney.
"Our hope is that can happen through the diplomatic process, but we've all learned that we need to be cautious and strong at the same time and our responses clear about what is acceptable and what is not acceptable," he added.
Russia's Itar Tass news agency reported on Tuesday that the aid convoy had set off from near Moscow and was expected to take two or three days to reach east Ukraine, about 1,000 km (620 miles) to the southwest.
Thousands of people are believed to be short of water, electricity and medical supplies because of the fighting. U.S. President Barack Obama said any Russian intervention without Kiev's consent would be unacceptable and violate international law.
Australian Foreign Minister Julie Bishop, who last month travelled to the United States to press for a U.N. resolution for an independent, international investigation into the missile strike that brought down Malaysia Airlines Flight MH17, killing all 298 people on board, also issued a stern warning.
"Any intervention by Russia into Ukraine under the guise of an humanitarian crisis would be seen for the transparent artifice that it is and Australia would condemn in the strongest possible terms any effort by Russia to enter the Ukraine under the guise of carrying out some sort of humanitarian mission," she told reporters.
Kerry and Bishop were speaking at a joint news conference with U.S. Defense Secretary Chuck Hagel and Australian Defence Minister David Johnston following annual Australia-United States Ministerial Consultations (AUSMIN) in Sydney.
(Reporting By Jane Wardell; Editing by Paul Tait and Robert Birsel)