BERLIN  — Germany and France pressed Russian President Vladimir Putin to do more to calm the situation in Ukraine and make May 25 presidential elections there possible, with Chancellor Angela Merkel insisting Saturday that Putin must send "more signals of de-escalation."

Merkel described sovereignty referendums planned Sunday by pro-Russian insurgents in two troubled eastern Ukrainian regions as "illegal," while French President Francois Hollande said they "carry no weight."

The rebels are going ahead with the referendum despite Putin's call on Wednesday to delay the vote.

Merkel said she and Hollande agreed to "make clear that the Russian president must send more signals of de-escalation so that (presidential) elections can take place."

"There have been initial signs, but this must be strengthened so that the message gets through to eastern and southern parts of Ukraine that everyone wants fair and general presidential elections," she added.

"If that doesn't happen, it would contribute to a further destabilization of Ukraine," Merkel said, stressing that European leaders would then be ready to toughen sanctions.

"We have relations with Vladimir Putin; we are using them so that he can take into consideration what is at stake over these coming weeks in Ukraine," said Hollande, who met Merkel in her Stralsund constituency in northeastern Germany.

Merkel and Hollande called in a joint statement for a "national dialogue" between the Kiev government and representatives of all Ukrainian regions, which they said should be open to all who reject violence. Merkel said she'd like to see it start next week.

The European Union has imposed targeted sanctions on Russian officials but has held back so far on all-out economic sanctions, and Hollande stressed he hopes to avoid that escalation.

France has stuck to a 3-year-old deal to provide two warships to Russia, the first set for delivery in October. On Saturday, Hollande said that the contract "is being carried out ... for the moment it is not called into question."