President Vladimir Putin sought on Saturday to give Russia's ruling party a pre-election boost by promising to spend big on infrastructure, education and health.

Putin, 68, also announced his key allies, the defence and foreign ministers, would front the campaign for the ruling United Russia party for September's parliamentary elections.

The jailed Alexei Navalny, Putin's most prominent domestic critic, and his allies, are barred from the elections after they were declared "extremists". 

Speaking at its party congress, Putin praised United Russia for its "ability to renew and constantly develop".

With real wages falling and inflation rising, its ratings are at a multi-year low, according to a poll by the Levada Center, an independent pollster. It showed just 27% of Russians supported the party in March, down from 31% in August.

Putin proposed Defence Minister Sergei Shoigu and top diplomat Sergei Lavrov to head the list of party candidates at the elections.