(CNN) -- Fierce fighting in eastern Ukraine has forced authorities to suspend the search for victims who died when Malaysia Airlines Flight 17 was shot out of the sky.
"The Dutch mission at the crash site of MH17 has stopped," Prime Minister Mark Rutte told reporters Wednesday.
Search teams plan to return to the plane crash site, Rutte said. But he didn't give a date of when that might happen.
"We have done what we could do in the current conditions," Rutte said. "Everyone will agree with us that we should not expose our people to unnecessary risk."
Constant shelling was heard north of Donetsk on Wednesday evening.
And small-arms fire came very close to the investigation team at the crash site Wednesday, forcing them to withdraw from the site, said Pieter-Jaap Aalbersberg, head of the recovery mission.
Searchers are disappointed they haven't been able to complete their mission, he said. But he said they did make significant headway, recovering human remains and personal belongings like photo albums, diaries and toys.
"We aim to return to the crash site as soon as we have the opportunity to work there for a longer period under stable conditions," he said.
Uptick in Donetsk violence
Ukrainian forces continued their attempt to take back control of the restive city of Donetsk from pro-Russian separatists Wednesday.
Russia's Foreign Ministry claimed in a statement Monday that the Ukrainian military was firing missiles and using multiple rocket systems in and around the city.
It accused Ukraine's government of wanting to continue the war and called for talks to find a political solution to the crisis.
With escalated fighting and Ukrainian forces making gains, the Russian deployment at the border could portend an intervention under the banner of a peacekeeping operation.
Russia asked the U.N. Security Council on Tuesday for an emergency hearing on the humanitarian crisis in Ukraine
Russian troop buildup
The buildup of Russian troops along the Ukraine border is raising concerns that Moscow might be contemplating another intervention similar to the one that annexed Crimea earlier this year.
According to a NATO official, Russia now has about 20,000 troops stationed "in an area along the entire border with eastern Ukraine." The buildup nearly doubled the troop deployment in the past week by adding 8,000 more forces to 12,000 already there, the official said.
In addition, Russia's Defense Ministry is staging a week of military exercises involving air troops and anti-missile defense forces. The exercises are taking place in Russia's southern Astrakhan region, roughly 500 miles from the border with Ukraine.
Similar military exercises preceded Russia's annexation of Crimea in March, which escalated the Ukraine conflict after the ouster of pro-Moscow President Viktor Yanukovych a month earlier.
Refugees flee conflict
The ongoing fighting has killed close to 1,400 people -- civilians and combatants -- and more than 4,000 people have been wounded in eastern Ukraine since mid-April, according to U.N. officials.
The fighting has also forced hundreds of thousands of people to flee their homes and seek shelter either elsewhere in Ukraine or across the border in Russia.
The U.N. refugee agency, the UNHCR, said Tuesday that the Russian authorities estimate that around 730,000 Ukrainians have sought sanctuary in Russia this year under a visa-free travel program. This includes more than 168,000 who have reported to Russia's Federal Migration Service.
UNHCR's European director, Vincent Cochetel, told journalists in Geneva that about 80% of the Ukrainians who have fled to Russia are staying in border areas, while others are with friends or family in other parts of the country.
Many people in eastern Ukraine are Russian-speaking and have strong ties to Russia.
At the same time, nearly 118,000 people are reported to be internally displaced, most of them from eastern Ukraine, based on information given to the UNHCR by Ukrainian authorities and local NGOs.
"In the past seven days more than 6,200 people have been forced from their homes," Cochetel said.
Many have fled with limited possessions, some driven out by the destruction of homes and infrastructure, while others say they fear being caught in the crossfire or suffering persecution.
John Ging, operations director of the U.N. Office for the Coordination of Humanitarian Affairs, called on all sides Tuesday to allow people to move freely and safely.
"The humanitarian situation is deteriorating, and the worrying increase in violence in urban areas puts a greater number of people at risk.
"Until violence is ended, we will continue to see an increase in human suffering, and in the number of people displaced. Immediate action is required to prevent this crisis from worsening," he said, according to prepared remarks.
CNN's Mick Krever and Anna Maja Rappard contributed to this story