WASHINGTON — President Obama said Monday that he would wait for the outcome of peace talks before deciding whether to provide lethal weapons to Ukraine. Such assistance would represent a striking break with European allies who say that arming the country against Russian aggression would make the conflict worse.

In a joint White House news conference with Chancellor Angela Merkel of Germany, Mr. Obama said he was hopeful that economic sanctions would persuade President Vladimir V. Putin of Russia to seize a diplomatic solution. But he said the United States would consider sending defensive weapons to Ukraine if European-led talks scheduled for this week did not produce peace.

“If, in fact, diplomacy fails, what I’ve asked my team to do is to look at all options,” Mr. Obama said. “What other means can we put in place to change Mr. Putin’s calculus? And the possibility of lethal defensive weapons is one of those options that’s being examined.”

Many leaders in European capitals share the Obama administration’s deep distrust of Mr. Putin, but they continue to hope that the pressure of economic sanctions will lead him to accept some sort of settlement. But the major Western European countries, including Britain, Germany and France, oppose sending arms.