WASHINGTON — The Obama administration on Thursday accused Russia of firing artillery from its territory into Ukraine to hit Ukrainian military sites and asserted that Moscow is boosting its supply of weaponry to pro-Russian separatists.
‘‘We have new evidence that the Russians intend to deliver heavier and more powerful multiple rocket launchers to separatist forces in Ukraine and have evidence that Russia is firing artillery from within Russian to attack Ukrainian military positions,’’ State Department spokeswoman Marie Harf told reporters.
Harf said the evidence derived from ‘‘some intelligence information’’ but declined to elaborate, saying it would compromise sources and methods of intelligence collection.
The allegations come amid an increasingly bitter war of words between Washington and Moscow over the crisis in Ukraine and conflicting claims over the downing of a Malaysian passenger jet over eastern Ukraine last week.
The United States has repeatedly accused Russia of stoking the Ukraine rebellion and has said it believes separatists shot down the Malaysian plane, killing nearly 300 people, with a Russian-provided surface-to-air missile.
Harf said Wednesday the ultimate responsibility for the downing of the plane rests with President Vladimir Putin and the Russian government.
President Obama said Thursday that the downing of the jet ‘‘may stiffen the spine of our European partners’’ as they consider additional sanctions against Russia.
In an interview on CNBC, Obama welcomed Europe’s earlier sanctions against Russia but said the actions have come ‘‘not always as fast as we’d like.’’
The European Union agreed Thursday to add more names to the list of Russians and pro-Russian Ukrainians subject to EU-wide asset freezes and travel bans. The EU is also considering broader measures that target key sectors of the Russian economy and could act on those penalties next week.
Washington is preparing to deepen its own sanctions against Russian banks, as well as energy and defense companies, and could levy those penalties next week.
In Ukraine, Australian and Dutch diplomats joined forces Thursday to promote a plan for a UN team to secure the plane crash site which has been controlled by pro-Russian rebels. Two more military aircraft carrying remains of victims arrived in the Netherlands.
Human remains continue to be found a full week after the plane went down — underlining concerns about the halting and chaotic recovery effort at the sprawling site spread across farmland in eastern Ukraine. Armed separatists control the area and have hindered access by investigators.
All 298 people aboard Malaysia Airlines Flight 17 — most of them Dutch citizens — were killed when the plane was shot down on July 17. US officials say the Boeing 777 was probably shot down by a missile from territory held by pro-Russian rebels.
Prime Minister Tony Abbott of Australia, who said he fears some remains will never be recovered unless security is tightened, has proposed a multinational force mounted by countries that lost citizens in the disaster. Abbott said Thursday he had dispatched 50 police officers to London to be ready to join any organization that may result.
Australia’s foreign minister, Julie Bishop, was traveling with her Dutch counterpart, Frans Timmermans, to Kiev to seek an agreement with the Ukraine government to allow international police to secure the wreckage, Abbott said.
Details including which countries would contribute and whether officers would be armed and protected by international troops were yet to be agreed, Abbott said.
International experts found more remains still at the crash site both Wednesday and Thursday, Michael Bociurkiw, a spokesman for the Organization for Security and Cooperation in Europe, told reporters in Donetsk on Thursday. The organization’s observers, sent to monitor the conflict, escorted a delegation from Australia to examine the wreckage Thursday for the first time. More Australian specialists are expected Friday, Bociurkiw said.
On Monday, the United Nations Security Council unanimously approved a resolution proposed by Australia demanding that rebels cooperate with an independent investigation and allow all remaining bodies to be recovered.
The first remains arrived in the Netherlands on Wednesday and were met by King Willem-Alexander, Queen Maxima, and hundreds of relatives. The two planes Thursday brought a total of 74 more coffins back to the Netherlands, said government spokesman Lodewijk Hekking.
Patricia Zorko, head of the National Police Unit that includes the Dutch national forensic team, said some 200 experts, including 80 from overseas, were working at a military barracks on the outskirts of Hilversum to identify the dead.
Zorko warned that the process of identification could be drawn out. ‘‘Unfortunately this type of investigation often takes time,’’ she said. ‘‘Count on weeks and maybe even months.’’