Volkswagen AG’s heavy-truck division set a deadline for Navistar International Corp. to accept its takeover bid, ratcheting up pressure on the U.S. manufacturer to decide on a $3.6 billion deal.

Volkswagen AG’s Traton truck-making division echoed competitors in warning it’s “intensively” preparing for a much more difficult environment next year.

Volkswagen AG raised 1.55 billion euros ($1.8 billion) selling a stake in its truck business, but only after pricing the offer at the low end of a target range to attract investors to one of Europe’s biggest initial public offerings this year.