China's central bank has suspended at least three foreign banks from conducting some foreign exchange business until the end of March, three sources who had seen the suspension notices told Reuters recently.

Included among the suspended services are liquidation of spot positions for clients and some activities related to cross-border, onshore and offshore businesses, the sources said.

The sources, speaking on condition that the banks were not named, said the notices sent to the affected foreign banks by the People's Bank of China (PBC) gave no reason for the suspension.

The PBC did not immediately respond to a request for comment.

Separately, three financial market sources in Europe said Deutsche Bank was one of the banks to have part of its foreign exchange business in China suspended.

The measure follows a slew of steps to steady the yuan since the Chinese government devalued the currency in August.

The spread between the onshore and offshore markets for the yuan, or renminbi, has been growing since the devaluation, making it increasingly difficult for the central bank to manage its currency and stem an outflow of capital from an economy that is facing its slowest growth in 25 years.

The sources told Reuters that authorities had warned the banks that if they engaged in lucrative carry trade, taking advantage of the different exchange rates, the central bank would move to further block arbitrage channels.

"This is part of the PBC's expedient means to stabilize the yuan's exchange rate," said an executive at a foreign bank contacted separately.

The sources said the banks might have been targeted due to the large scale of their cross-border forex businesses.

An economist at a top government think tank said the measure was a temporary bid to curb demand for dollars that has been strengthening towards the end of the year as the gap between the onshore and offshore yuan exchange rates widens.

"They hope to ease foreign exchange buying pressure and ease depreciation pressure on the yuan," said the economist who declined to be identified by name.

"But I don't think the authorities will take very strong capital control measures, they are likely to reinforce the existing measures."

The move could also ease pressure on the PBC for direct intervention in offshore markets to support the yuan, which has contributed to a fall of more than $400 billion in China's foreign exchange reserves this year.