A Spanish Civil Guard stands outside the Madrid branch of China's biggest lender, ICBC, in Madrid on Wednesday. The bank is under investigation for alleged money laundering, according to Spain's Interior Ministry. Photo: CFP

Spanish police on Wednesday searched the Madrid branch of China's biggest lender ICBC as part of a probe into the suspected laundering of at least 40 million euros ($44.5 million), police said in a statement.

The director of the branch and a deputy director were arrested, a source close to the investigation said.

"The Chinese Embassy in Spain will follow the development of this matter closely. We will exercise our rights to visit the people involved when it is necessary. Chinese people in Spain should not worry too much about this matter, and media should quote their source strictly in their reports," said Zhu Jian, the consular counselor from the Chinese Embassy in Spain.

The bank is suspected of being used to "introduce into the financial system funds earned through the alleged crimes of smuggling, tax fraud and the violation of workers' rights, allowing the transfer of the funds to China in a way that appeared legal," the police statement said.

The operation is part of a probe carried out last year against Chinese organized crime groups based in Madrid which are suspected of importing huge amounts of goods from China without declaring them on customs forms, to avoid import and tax duties.

The crime groups allegedly deposited the money earned into ICBC, which is accused of sending the funds to China without checking their origin as required by law.

One of the crime groups that was broken up last year is suspected of having laundered "an amount known to be as of the moment 40 million euros" in the branch, the police statement said.

The bank's Madrid office could not be reached by the Global Times for comment by press time on Wednesday.

A Beijing-based spokesman for ICBC told Reuters late Wednesday night that the bank was paying close attention to the investigation.

"Our Madrid branch is actively cooperating," he said.

"Strictly implementing anti-money laundering regulations, and strictly operating within the law and regulations have always been our fundamental operation and management principles," the spokesman noted.

Ouqiao.es and Shan Jing contributed to the story