NATO's top commander said Wednesday that Russia was "increasing" the number of troops and weaponry along the border with Ukraine.

"The number of troops along the (Ukrainian) border is increasing. It is well over 12,000," General Philip Breedlove told reporters at the end of his one day visit to Kosovo, where he inspected the alliance's peacekeeping mission.

U.N. Secretary-General Ban Ki-moon on Wednesday called on Kiev and pro-Russian rebels to immediately stop fighting to allow investigators to reach the crash site of the downed Malaysian plane.

"The families of this horrific tragedy deserve closure and the world demands answers -- international teams must be allowed to conduct their work," said Ban in a statement released by his spokesman.

Australia's priority was gaining access to the crash site of downed Flight MH17 in Ukraine, not imposing sanctions on Russia, Prime Minister Tony Abbott said Wednesday.

The United States and Europe announced tough new sanctions targeting Russia's key financial, arms and energy sectors on Tuesday in response to Moscow's intervention in the Ukraine crisis.

The father of a British MH17 victim said fighting in the Ukrainian plane crash zone should end to facilitate the repatriation of victims, after he met Prime Minister David Cameron on Tuesday.

Barry Sweeney, whose son Liam was among the 298 people killed, spoke of his anger and frustration at not knowing what had happened to the 28-year-old's body.

Seventeen people, including three children, were killed in the past 24 hours by shelling in Ukraine's rebel-held stronghold of Gorlivka, local Ukrainian officials said on Tuesday.

A statement said that 43 people were also wounded in the city which was observing three days of mourning for 13 civilians including 2 children killed on Sunday by Grad rockets.

Observers from the Organization for Security and Cooperation in Europe were set to arrive in southern Russia Tuesday on their mission to monitor two border crossings with rebel-held Ukraine, the OSCE said.

The first members of the team of 16 civilian monitors were due to arrive in Russia's Rostov region where they were expected to hold meetings with officials from the regional administration, border guards and customs service, said OSCE spokeswoman Tatyana Baeva.

The European Union finally agreed Tuesday to impose broad economic sanctions against Russia, hoping to force Moscow to reverse course in Ukraine, EU officials said, as the U.S. slapped sanctions on three banks.

The new European measures impose restrictions on the finance, defense and energy sectors so as to increase the cost to Russia of its continued intervention and support of pro-Moscow rebels in Ukraine.

The United States has found that Russia violated a 1987 arms control treaty by testing a ground-launched cruise missile, a senior U.S. official said late Monday, calling the matter "very serious." 

The finding comes in a 2014 report that concluded Russia was in violation of the Intermediate-Range Nuclear Forces Treaty, which barred it from possessing, producing or flight-testing such cruise missiles with a range of 500 to 5,500 kilometers, the official told Agence France Presse.

The leaders of the United States, Germany, France, Britain and Italy agreed Monday on the need to impose new sanctions on Russia over its presumed role in Ukraine's insurgency, the French presidency said.

President Barack Obama, Chancellor Angela Merkel, President Francois Hollande, Prime Minister David Cameron and Prime Minister Matteo Renzi "confirmed... their intention to adopt new measures against Russia," the French presidency said after the five leaders held telephone talks.

With their sunburnt backs, flip-flops and baseball caps, the families lolling about the Ukrainian resort town of Sjedove on the Azov Sea could be mistaken for holidaymakers.

But they are all refugees, fleeing the deadly combat in east Ukraine as the fighting has escalated in recent days and come closer and closer to large cities.