In the railway town of Debaltseve, Ukraine’s cease-fire lasted all of 40 minutes. “We were surprised when the firing stopped, and hoped it would be the cease-fire,” said Albert Sardaryan, a 22-year-old combat paramedic in the town, by telephone. “But then it started again.” Fighting for Debaltseve has become the biggest challenge to the cease-fire that went into effect at midnight Saturday and was supposed to end months of conflict between Ukrainian forces and Russia-backed militants in Ukraine’s east. A separatist advance supported , according to U.S. and Ukrainian officials, by Russian army units, has all but cut off thousands of Ukrainian soldiers in the town. German Chancellor Angela Merkel on Monday described the situation in Ukraine as “fragile” and called on all sides […]