By Thomas Escritt

BERLIN (Reuters) - German legislators are demanding an explanation from a senior Social Democrat on the parliamentary committee that scrutinises the work of the intelligence services after he held undisclosed talks with close associates of Russia's president.

Ralf Stegner, a member of the Bundestag's Parliamentary Control Committee, was among politicians from the SPD and Chancellor Friedrich Merz's conservatives who took part in the April meeting in Baku.

Among those they met on April 13 in the Azerbaijan capital was former Russian Prime Minister Viktor Subkov, head of Gazprom's supervisory board, and Valery Fadeyev, EU-sanctioned chair of Russia's human rights council.

On both sides, the participants were former members of the Petersburger Dialogue, a forum founded in 2001 by Russian President Vladimir Putin and then-Chancellor Gerhard Schroeder. The forum was officially disbanded in 2021 after Russia's crackdown on several participating civil society organisations.

Four German participants - Stegner, Ronald Pofalla - who once led former Chancellor Angela Merkel's office - and two former regional ministers - confirmed in a statement to Reuters that they had been at a "private" event in Baku.

"Talking even in difficult times of growing tension is a fundamental principle of good foreign policy," they wrote, adding that the "confidential" meeting was not secret, and none of them had a public mandate to be there or had been paid for their presence.

The meeting, first reported by ARD public television and newspaper Die Zeit, took place at a time when Russia's ties with the EU are in a deep freeze over its invasion of Ukraine. The timing raised questions over the apparent willingness of some politicians to seek rapprochement even as Moscow wages war on a German ally.

In Stegner's case, critics also raised security concerns: Members of the parliamentary control committee have privileged, confidential access to the work of Germany's foreign and domestic security services, both of them heavily involved in gathering intelligence relating to Russia and the war.

"This is a quite impossible and irritating development that must immediately be cleared up," Konstantin von Notz, the Green chair of the committee, told Der Spiegel.

Roderich Kiesewetter, a conservative member of the committee, said Stegner should explain himself, while liberal European legislator Marie-Agnes Strack-Zimmermann said Stegner should not be nominated for a new term on the committee.

"People in such a key role have to be above all suspicion," she told Funke newspapers. "That is not the case for him."

(Additional reporting by Andreas Rinke, editing by Philippa Fletcher)