President Vladimir Putin has hailed his “very good relationship” with François Fillon, praising the frontrunner in the French centre-right primary contest on his plans for a rapprochement with Moscow.

The comments underline the close ties between the Russian leader and the French politician, who would be well placed to become president of France next year if his nomination as the centre-right’s candidate were confirmed.

Days before a run-off vote between Mr Fillon and Alain Juppé to decide who will be the centre-right candidate, they also reflect Russia’s wider effort to cultivate ties with like-minded European politicians to end its diplomatic isolation.

But the comments from Mr Putin also highlight a closeness to Russia that some of Mr Fillon’s critics say is a potential vulnerability for his campaign at a time of widespread hostility in France to Russia’s military intervention in Syria.

Mr Fillon is advocating a dramatic change of tack with Moscow, favouring lifting economic sanctions imposed by the EU after Russia’s annexation of Crimea. He is also pushing for a military alliance with Mr Putin and the Syrian regime of Bashar al-Assad to combat Isis.

Jean-Marc Ayrault, France’s foreign minister, lashed out at Mr Fillon’s foreign policy proposals. “Of course we have to talk to Russia. We talk to Russia all the time,” Mr Ayrault said in Paris. “But that doesn’t mean we should align ourselves with Russia.”

Mr Juppé also criticised Mr Fillon’s “extreme kindness for Putin” as he sought to rally voters ahead of the run-off on Sunday.

Mr Fillon, who was prime minister under Nicolas Sarkozy’s presidency, met Mr Putin regularly between 2008 and 2012 when the Russian leader was serving as prime minister.

On Wednesday, Mr Putin was full of praise for Mr Fillon. “For all his European manners, in the best sense of that word, he is always able to argue for his point of view in a very tough and consistent manner, in that sense he is a tough negotiator. But of course he is a highly professional and decent man,” Mr Putin said in Moscow.

The Russian leader said he welcomed the shift in sentiment. “For our part we will do everything to facilitate [better relations],” he said.

Diplomatic ties between the two countries have deteriorated during President François Hollande’s time in office. The French leader spearheaded economic sanctions on Russia after it annexed Crimea and, with Angela Merkel, the German chancellor, has pushed for a ceasefire in eastern Ukraine and a political resolution of the conflict.

Mr Hollande has also condemned Russia’s military support for the Syrian regime of Mr Assad, describing the bombing of civilians in Aleppo as “war crimes”. Last month, Russia vetoed a UN Security Council resolution, drafted by France, that demanded an end to air strikes and military flights over the Syrian city.

Responding to Mr Fillon’s suggestions of lifting economic sanctions, Mr Ayrault said: “Do you think that it is out of pure pleasure that we impose sanctions? No, they are there because eventually there is a negotiation and an accord. That’s how it works.”