After the rocket attack against a residential neighbourhood in Mariupol, killing at least 30, there have been strong condemnations from around the world.
In a statement, the Swedish Prime Minister Stefan Löfen said: "This attack by the Russia-backed separatists, together with their announcement of a renewed offensive in eastern Ukraine, is highly concerning. They run counter to all commitments made and undermine efforts to find a solution to the crisis".
"Together with its European Union partners, Sweden expects Russia to immediately stop its support to the separatists and use all its influence to prevent continued fighting. Further escalation would lead to a further grave deterioration of relations between the EU and Russia," he said.
Foreign Minister Margot Wallström spoke to her Ukrainian colleague Pavlo Klimkin on Saturday. The country is pleading for more humanitarian help, which Sweden will respond to.
In an interview with the news agency TT on Sunday, Wallström said that "the situation is very bad seen from our efforts to steer the development in the right direction". She pointed to Russia's silence on the matter as a problem.
What options do you see that the EU has to increase the pressure on Russia? asked TT's reporter.
"The immediate reaction is to use the tools we have, including sanctions, and to make them even stricter. I think the EU is willing to review all its tools," she said.
Meanwhile Donald Tusk, the Polish president of the European Council, tweeted: "Once again, appeasement encourages the aggressor to greater acts of violence. Time to step up our policy based on cold facts, not illusions."
Russia, however, has repeatedly denied arming separatists or deploying regular troops in the region.