Russia's largest mobile network provider, MTS, has signed a deal with the Chinese telcom giant Huawei to build 5G internet in Russia.

The move is creating a further divide in the tech cold war between the US and China, which has already seen the US bar American tech firms from working with their Chinese counterparts.

The MTS-Huawei deal came as Chinese President Xi Jinping visited Russian President Vladimir Putin in Russia and called Putin his "best and bosom friend."

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Russia's largest network provider has signed a deal with the Chinese tech giant Huawei to build 5G internet, creating a further divide in the tech cold war rocking the US and China.

The agreement, signed Wednesday between Russia's MTS and Huawei, will "promote 5G technology and launch pilot 5G networks in Russia in 2019-2020," Huawei said in a statement sent to Business Insider.

The deal came on the first day of Chinese President Xi Jinping's three-day trip to Russia to meet with Russian President Vladimir Putin. The signing ceremony "took place at the intergovernmental level" in the Kremlin while the two leaders looked on.

It is a prominent escalation of the cold war between Washington and Beijing, which has seen the US bar American tech firms from working with their Chinese counterparts.

In return, China has amped up efforts to supersede the US in artificial-intelligence research, and the two sides have imposed tit-for-tat trade tariffs against each other.

President Donald Trump's administration officially designated Huawei a national security threat last month.

Secretary of State Mike Pompeo has threatened the US's European allies with consequences if they do not distance themselves from the Chinese company.

Read more: The Trump administration is warning allies to stay away from a powerful Chinese company — but not everyone's listening

Putin and Xi at a friendly match between Russian and Chinese youth ice-hockey teams in Tianjin, China, in June 2018. Ng Han Guan - Pool/Getty Images

Putin, 'my best and bosom friend'

As the Trump administration ramps up its attacks on Beijing, the China-Russia relationship appears stronger than ever.

Xi arrived in Moscow on Wednesday, and the two leaders traveled to St. Petersburg together on Thursday to attend the St. Petersburg International Economic Forum, which outlets including Bloomberg, The Moscow Times, and Agence France-Presse describe as the "Russian Davos."

Jon Huntsman, the US ambassador to Russia, was among US government officials who refused to attend this year's forum to protest the prosecution of Michael Calvey, an American investor in Russia who was detained and accused of embezzlement earlier this year.

Xi and his "best and bosom friend" Putin made Russian food together. AP

Xi on Tuesday gave a lengthy interview to Russia's state-run TASS news agency, in which he lauded Chinese-Russian ties and called Putin his "best and bosom friend."

Here's what Xi said about his apparent bromance with the Russian president:

"Since 2013, President Putin and I have met nearly 30 times on bilateral and multilateral occasions, and talked on the phone and written to each other many times. I keep fond memories of each interaction I had with President Putin.

"We have had in-depth and most wide-ranging exchanges on both major issues like the international situation, bilateral ties and governance, and more light-hearted topics like literature, art, and sports.

"We have taken a high-speed train ride together, watched an ice-hockey friendly between Chinese and Russian youth teams, celebrated his birthday in Bali, exchanged phone calls and congratulatory messages on each other's important festivals, and been awarded medals of the highest honor by each other's countries.

"I have had closer interactions with President Putin than with any other foreign colleagues. He is my best and bosom friend. I cherish dearly our deep friendship."

Xi and Putin on Wednesday also upgraded their countries' relationship from bilateral ties to a "comprehensive strategic partnership of coordination in new era," the South China Morning Post reported.

Xi and Trump are expected to meet again at the G20 summit in Japan later this month.

US President Donald Trump and Putin in Helsinki, Finland, in 2018. Grigory Dukor/Reuters

China granted 5G licenses to its largest state-owned telcom operators on Thursday, the Financial Times and The Wall Street Journal reported, accelerating the nation's rollout of the high-speed mobile network technology.

Experts have warned that the US's war on Huawei could leave the country lagging behind in the global race for faster internet.

"The United States will not get a second chance to win the global 5G race," said Meredith Attwell Baker, the head of the CTIA telecoms trade association, in an April report.