Vladimir Putin has warned against foreign meddling in Russia's politics in a speech designed to spell out his priorities for the year ahead.

"Direct or indirect meddling in our domestic politics is unacceptable," Putin told a gathering of about 1,000 politicians in the Kremlin's grand St George Hall on Wednesday. "A figure who receives money from abroad for his political work, and thus serves some foreign interest, cannot be a politician in Russia."

The Russian president's comments build on a year-long campaign designed to paint members of the growing opposition to him as agents of the west.

It was a rare moment of attack in a 90-minute speech in which Putin was more calm and subdued than usual. Amid rumours of back trouble, the 60-year-old leader often leaned on the podium as he addressed the crowd.

In the first major gathering in months, the opposition is planning to march on Saturday to Moscow's Lubyanka, the building that was the base of the Soviet-era KGB and now houses its successor, the FSB. Dozens of activists have been arrested and dozens more questioned in a far-reaching campaign designed to strike fear into those who dare protest against Putin.

He used his speech to pay lip service to liberal ideals. "Russia does not and cannot have any political choice but democracy," he said. "I want to say, and even stress, that we share those universal democratic principles taken around the whole world."

The opposition to Putin arose after he announced his intention to return to the presidency after four years as prime minister. Activists complained of widespread fraud in the elections.

Putin acknowledged that something was missing in Russian society, and lay the blame at an absence of moral values: "It's painful for me to talk about this today, but I am required to say this. Today, Russian society has a clear deficit of spiritual principles – mercy, compassion, mutual suffering and support – a deficit of that which through all of history made us stronger, which made us proud."

He called on officials to "strengthen the strong spiritual and moral fabric of society" and to reinstate patriotism in Russian schools.

He urged Russian businesses to be patriotic and called for the "de-offshore-isation" of the Russian economy, referring to the fact that many Russian businesses are owned via shell companies in order to avoid taxes.

Putin attempted to convey that his recently launched anti-corruption campaign was a serious move to clean up the country's notoriously corrupt government. He said politicians and their close relatives should be banned from keeping money in foreign banks or owning shares in foreign companies. As the crowd began to clap, he stepped in to say: "Wait to applaud, you might not like what comes next."