Germany's would-be next chancellor, Friedrich Merz, won lawmakers' approval to loosen strict debt rules for higher defense spending as doubts mount about the strength of the trans-Atlantic alliance.

Germany's parliament approved plans for a massive spending surge on Tuesday, throwing off decades of fiscal conservatism in hopes of reviving economic growth and scaling up military spending for a new era of European collective defence.

Under Germany's constitution, Merz needs a two-thirds majority to get the changes passed. With the support of the Greens and Social Democrats, he should succeed. Urgent motions by both the AfD and the Left to challenge next week's sessions of the outgoing parliament failed at the constitutional court on Friday, enabling the vote to go ahead.