Tensions soared Wednesday between the United States and two of its NATO partners, Germany and Turkey, as the alliance opened a 70th birthday celebration aimed at showing a united front against a resurgent Russia.

"Germany must do more. And we cannot ensure the defense of the West if our allies grow dependent on Russia," Pence told a think-tank forum on the NATO anniversary.

"It is simply unacceptable for Europe's largest economy to continue to ignore the threat of Russian aggression and neglect its own self-defense and our common defense," he said.

President Donald Trump has repeatedly voiced annoyance that few allies in the North Atlantic Treaty Organization are meeting a goal set by the alliance in 2014 for each member to devote two percent of GDP to defense.

Germany last month announced that defense spending would slip to 1.25 per cent in 2023.

Hungry for energy, Germany has also defied the United States and several Eastern European states by forging ahead with Nord Stream 2, a gas pipeline with Russia that will double the capacity of the existing link.

"If Germany persists in building the Nord Stream 2 pipeline, as President Trump said, it could turn Germany's economy into literally a captive of Russia," Pence said.

Pence, however, promised that the United States "is now and will always be Europe's greatest ally" -- a tonal shift from Trump, who has loudly wondered whether it is worth defending smaller NATO members such as Montenegro.

German Foreign Minister Heiko Maas, speaking at Columbia University in New York before heading to Washington, denied Germany was dependent on Russia.

"Germany is very involved with different NATO missions and we will fulfill our commitments. Germany can be relied upon," he said.

Western powers have also increasingly clashed with Turkish President Recep Tayyip Erdogan's Islamist-rooted government, which has cracked down on dissent at home and threatened to strike US-backed Kurdish fighters in Syria.

On Monday, the United States said it was suspending Turkey's participation in the F-35 fighter-jet program due to Ankara's plans to buy Russia's S-400 missile defense system, raising fears that Moscow could gain data to hone its hardware and shoot down Western aircraft.

"Turkey must choose -- does it want to remain a critical partner of the most successful military alliance in the history of the world, or does it want to risk the security of that partnership by making reckless decisions that undermine our alliance?" Pence said.

But Turkish Foreign Minister Mevlut Cavusoglu ruled out a change of heart, saying: "The S-400 deal is a done deal and we will not step back from this," he said.

Cavusoglu said Turkey still backed NATO on core concerns with Russia and would never recognize Moscow's 2014 takeover of Crimea from Ukraine. "We have been working with Russia," he said.

"But it doesn't mean that we are undermining the alliance and we agree with Russia on everything. There is no shift on our foreign policy."

The 70th anniversary comes amid rising concern over Russia, which has supported separatists in Ukraine and Georgia and sought to sway the 2016 US election.

NATO Secretary General Jens Stoltenberg, in an address to the US Congress, said the alliance wanted better relations with Russia -- but needed to prepare a strong defense.

"We do not want a new arms race. We do not want a new Cold War. But we must not be naive," Stoltenberg said.

Stoltenberg appeared to soothe Trump during a White House meeting on Tuesday, crediting the US leader's tough rhetoric with pushing the Europeans and Canada to bolster their defense budgets by USD100 billion between 2016 and 2020.

Lawmakers repeatedly rose to standing ovations as Stoltenberg hailed the value of the alliance.

"NATO has been good for Europe, but NATO has also been good for the United States," he said.

"The strength of a nation is not only measured by its economy or the number of its soldiers, but also by the number of its friends. And through NATO, the United States has more friends and allies than any other power.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)