Telefonica Deutschland, one of three German telecommunications providers said on Wednesday that it has picked Chinese tech giant Huawei alongside Finland's Nokia to build its expanding 5G network.

The decision by the branch of Spain's Telefonica, a telecommunications giant headquartered in Madrid, comes amid heated debate in Germany over whether to allow Huawei to enter the 5G market of Germany.

German Chancellor Angela Merkel expressed before that she doesn't want to bar Huawei as long as it abides by certain security standards.

This October, Germany left a 5G network door open for Huawei by releasing the rules on the safe construction and operation of the country's telecommunications networks.

Berlin wants to toughen up technical certification and scrutiny of a vendor's governance, while lawmakers are still considering whether to introduce additional parliamentary oversight.

"We hope that this window of uncertainty will be as short as possible - we don't yet have certification for any of our vendors," Telefonica Deutschland CEO Markus Haas told reporters on a conference call.

Germany's other two mobile operators - market leader Deutsche Telekom and Vodafone - are existing customers of Huawei but have yet to publicly confirm whether they will stick with the Shenzhen-based network's leader for 5G.

Work should start in early 2020, and Telefonica Deutschland said it expected to have 5G up and running in Berlin, Hamburg, Munich, Cologne, and Frankfurt by the end of 2021. A year later, 30 cities with a population of 16 million would be covered.

"As a member of multiple global 5G standards organizations, Huawei has been deeply involved in 5G network security from the start, and has ensured cybersecurity is embedded in its network development and deployment practices," Huawei said in a statement before.

(With input from Reuters)