US says evidence shows Russia fired artillery into Ukraine
The US says it has evidence that Russia has fired artillery across the border targeting Ukrainian military positions.
Russia also intends "to deliver heavier and more powerful multiple rocket launchers" to pro-Russian separatists in Ukraine, the state department said.
Russia has frequently denied sending any rocket launchers into Ukraine.
The US comment comes a week after Malaysia Airlines flight MH17 crashed in eastern Ukraine, with the rebels widely accused of shooting it down.
Multinational efforts to find the cause of the crash are under way, led by the Netherlands which lost 193 of its citizens. All 298 people on board the flight died in the crash.
Dutch Prime Minister Mark Rutte has announced 40 unarmed military police are being sent to the crash site as part of efforts to find the last MH17 victims.
He said there would be more people working on the crash site and his government was looking at ways to make it more secure.
The US, which has repeatedly accused Russia of fuelling separatist sentiment in eastern Ukraine, says it believes that rebels shot down flight MH17 with a Russian-provided SA-11 Buk surface-to-air missile, probably by mistake.
Leading rebels in eastern Ukraine have given conflicting accounts of whether they had control of a Buk launcher at the time the plane was downed.
State department spokeswoman Marie Harf told reporters on Thursday the US had evidence derived from "some intelligence information" showing Russia firing artillery into eastern Ukraine.
She said the US would not provide further details so as not to compromise sources and methods of intelligence collection.
Buk surface-to-air missile system
Also known as SA-11 Gadfly (or newer SA-17 Grizzly)
Russian-made, mobile, medium range system
Weapons: Four surface-to-air missiles
Missile speed (max): Mach 3
Target altitude (max): 22,000 metres (72,000ft)
Source: Global Security
Earlier on Thursday, the EU said it was adding 15 people and 18 entities to the list of sanctions against Russia and Ukraine, in a move condemned by Russia's ambassador to the UK as "illegal, unreasonable and counterproductive".
It comes as two more planes carrying the remains of some of the passengers and crew of flight MH17 arrived in the Netherlands for forensic identification at a barracks south of the Dutch city of Hilversum.
Dutch investigators have faced difficulties gaining access to the rebel-controlled crash site in eastern Ukraine, amid continuing fighting there.
Some OSCE monitors and investigators who did manage to visit the site say there is a discrepancy in the numbers of bodies counted on the ground.
With remains still being found one week on, experts warn it could be months before all victims are identified.
Australian Prime Minister Tony Abbott has proposed a multinational force to secure the crash site mounted by countries most affected by the disaster, namely Australia, the Netherlands and Malaysia.
Foreign Minister Julie Bishop and her Dutch counterpart, Frans Timmermans, are in Kiev to try to secure agreement from the Ukrainian authorities for a Dutch-led police mission at the crash site.
Meanwhile, UK aviation investigators have managed to successfully extract data from the plane's two black boxes, the Dutch Safety Board, which is leading the investigation, said on Thursday.
They are looking for voice recordings of the last moments of the plane's flight, as well as potentially vital information from after any missile strike, which could yield clues about the impact and effect of the strike.
Details of further EU sanctions on Russia and Ukraine are expected to come to light on Friday, with talks on stepped-up action - which may include a ban on buying debt or stock issued by Russia's largest banks - also due to continue.
In other developments on Thursday:
- Ukrainian PM Arseniy Yatsenyuk resigned in protest at the disbanding of the ruling parliamentary coalition, paving the way for new elections. It is not yet clear if his resignation will be accepted by parliament
- CNN says one of its freelance journalists, Anton Skiba, was abducted by armed pro-Russia separatists in Donetsk on Tuesday and has appealed for his release
- Overall rebel military commander Igor Strelkov says in statement he has withdrawn his fighters from the outskirts of Donetsk
The fighting in eastern Ukraine erupted in April and is believed to have claimed more than 1,000 lives.