NEW DELHI — India’s defense minister is visiting Moscow this week to finalize the purchase of a Russian missile defense system, Indian officials say, in a weapons deal that would violate American sanctions against Russia.

The potential $6 billion deal comes at a time when the Trump administration is both weighing more extensive sanctions against Russia and trying to forge a military alliance with India. Indian officials say the agreement could be finalized as soon as this week, with India purchasing five S-400 Triumf systems, an antiaircraft missile array that can also intercept missiles.

If the purchase goes through, the Trump administration would have to choose between punishing India for violating the sanctions or granting an exemption to avoid souring the relationship.

The United States has been trying to cultivate India as a strategic ally and a hedge against Chinese military expansion. Washington has typically dangled defense deals as a way to improve military ties with countries, and it has courted India aggressively. Lockheed Martin offered last summer to move the production of F-16 fighter jets from Texas to India if India agreed to buy the plane.