WASHINGTON (AP) — President Barack Obama and French President Francois Hollande on Friday discussed developments in Ukraine and the terrorist threat posed by the group Boko Haram in Nigeria, two of the more prominent international crises facing them.

The White House said the two leaders spoke by phone to reiterate their stance that Russia would face additional sanctions if it provokes more instability on neighboring Ukraine. The White House said Obama praised the Kiev government's plans for presidential elections later this month.

The call came a day after Russian President Vladimir Putin informed European leaders that Russia will deliver gas to Ukraine next month only if it pays in advance. Putin said Ukraine's gas debt to Russia has kept rising and reached $3.5 billion.

Obama and Hollande also discussed a regional conference on Saturday in Paris that seeks to improve cooperation to combat threats posed by Boko Haram, the group that abducted nearly 300 girls in Nigeria.

France is among several Western countries that have given Nigeria expert assistance to help in the rescue of the missing girls.