Russian-backed rebels pushed forward yesterday with a new offensive that has brought all-out war back to eastern Ukraine after a five-month cease-fire, bringing U.S. and European threats of tighter Western financial sanctions against Moscow. Washington and Brussels are both considering new measures after accusing the Russian government of openly supporting the latest rebel advance in Ukraine with money, arms and troops on the ground. Ambassadors of NATO countries and Ukraine were due to meet in Brussels to discuss a response to the fighting, their first such emergency meeting since last August. Moscow denies playing a military role, and Russian President Vladimir Putin has accused Kiev of prolonging the conflict by refusing to talk to the rebels. He also said a "foreign NATO legion" was fighting alongside Ukrainian forces.The government in Kiev said it had ordered a state of emergency across the two rebel-dominated provinces and placed all Ukrainian territory on high alert.Its military said seven Ukrainian soldiers had been killed and 24 wounded in intensified clashes on Monday, with heavy fighting at Debaltseve, a small town the rebels have vowed to seize to safeguard their main strongholds.Violence in eastern Ukraine is at by far its worst since a ceasefire was agreed last September. Casualties have mounted, including in the major port of Mariupol where Kiev says 30 civilians were killed in rebel shelling on Saturday.After months during which the truce was punctured by small-scale skirmishes on the front line, rebels fighting for territory which the Kremlin calls "New Russia" said last week they were left with no choice but to launch an advance. Their main aim, they say, is to push back government forces that had been shelling rebel-held cities.The Kiev government sees the rebel advance as a repudiation of the ceasefire, restarting a war in which 5,000 people have been killed. Kiev and NATO believe thousands of Russian troops are in eastern Ukraine fighting on the rebels' behalf with advanced weapons, despite Moscow's denials.After months during which European politicians were discussing whether to start easing sanctions on Russia, the return of fighting to eastern Ukraine has suddenly shifted the debate to how to tighten them. Sanctions and the falling oil price have caused serious economic damage to Russia, with the rouble currency tumbling over the course of the past two months.U.S. President Barack Obama said Washington was considering all options short of military action to isolate Russia, and would act jointly with European partners."We are deeply concerned about the latest break in the ceasefire and the aggression that these separatists -- with Russian backing, Russian equipment, Russian financing, Russian training and Russian troops -- are conducting," Obama told a news conference during a visit to India on Sunday.