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.

"I'm sure that United Russia sets the highest bar for itself, which is to confirm its leadership position and to clinch a win at the elections," he said.

Putin did not name Dmitry Medvedev, the party leader and former president and prime minister, among the top candidates. Opinion polls have shown Medvedev has a low popularity rating.

Andrei Kolesnikov, a senior fellow at the Carnegie Moscow Center, said Lavrov and Shoigu were the most popular ministers.

"It's enough to show those two guys to the population, and it's obvious that this is Putin's party," he said.

Putin proposed extending an infrastructure loans programme until 2026 and a 100 billion roubles ($1.4 billion) pandemic recovery programme.

"People's well-being is of the highest value," he said.

He also pledged more funds for road construction and reiterated his support for a ban on exports of some kinds of timber from Jan 1. 2022.

Putin helped found the United Russia party 20 years ago, but has never been a member.