BERLIN — American and Russian negotiators have concluded a round of nuclear arms control talks in Vienna, aimed at producing a new agreement to replace the New START agreement that expires in February — the last remaining pact constraining the arsenals of the world’s two major nuclear powers.

U.S. negotiator Marshall Billingslea told reporters Tuesday that a day of high-level “marathon discussions” ended late Monday night and had been productive enough to conclude with the establishment of several technical working groups to delve deeper into the issues with the idea of paving the way for a second round of talks by late July or early August.

“We both agreed at the termination of our talks that the strategic environment has changed significantly since the New START treaty was signed,” he told reporters. “We can all remember back 10 years ago, the world is, in fact, a radically different place.”

New START, signed in 2010, imposes limits on the number of U.S. and Russian long-range nuclear warheads and launchers.

It became the last nuclear arms pact between the two nations after the U.S. last year scrapped the Intermediate-Range Nuclear Forces Treaty with Russia, a Cold War-era agreement that both sides had repeatedly accused the other of violating.

The INF Treaty was also criticized because it did not cover China or missile technology that did not exist a generation ago.

New START can be extended by five years by mutual consent.

Sergei Ryabkov, the Russian deputy foreign minister who led his country’s delegation in Vienna, told reporters in Moscow that he had reiterated the position that it should be.

“We presented our view and will keep doing so,” Ryabkov told the Interfax agency. “We are running out of time.”

He added, however, that the establishment of working groups was “a significant step forward” and said the talks were conducted in a positive atmosphere and reflected a shared desire to move forward.

U.S. President Donald Trump has called New START “just another bad deal” made by the Obama administration, and it was not clear whether he would agree to an extension.

Billingslea told reporters at a press conference held by the American delegation that any new agreement must include all nuclear weapons and not just strategic nuclear weapons, and also subject China to restrictions.

All options, he said are “definitely on the table.”

“Our ultimate decision, which is in the hands of the president, whether he decides to extend the New START treaty or allow it to run its course, is going to be very much driven by the extent to which we have made progress, not just with our Russian colleagues but with our Chinese counterparts,” he said.

In Brussels, NATO Secretary General Jens Stoltenberg said he would prefer China to be part of any future agreement, but that in the absence of that extending New START is the right thing to do.

“We should not end up in a situation where we have no agreement,” he said.

Billingslea said China had refused an American invitation to be part of the Vienna talks, but that he hoped the international community would pressure Beijing to take part in the future.

“The United States is not engaged in an arms race,” Billingslea said. “Of course we will not be left behind, but we seek to avoid this, and this is why a three-way nuclear arms control deal, in our view, has the best chance of avoiding an incredibly destabilizing three-way nuclear arms race.”

Ryabkov said Russia believes that other nuclear powers should join future nuclear arms deals, but added that a decision to join could only be voluntary.

“We are well aware of China’s position, we respect it and we don’t see any sign that the Chinese position could change in the direction the U.S. desires in a foreseeable perspective,” he said, according to Interfax.

Billingslea said he “wouldn’t rule anything in or out” but that the U.S. did not think Britain or France, with much smaller nuclear arsenals, should be included like he said Russia wanted.

“Both qualitatively and quantitatively the United Kingdom and France are in a very different situation than the arms racing Chinese,” he said.

The U.S. attempt to bring China on board got off to an awkward start when Billingslea on Monday tweeted a photo of the negotiating table set up with Chinese flags in front of vacant seats, saying “China is a no-show.”

Chinese Foreign Ministry spokesman Zhao Lijian lashed out Tuesday, saying it was “neither serious nor professional for the United States to attract attention in this way.”

“We urge the U.S. to stop this boring trick, actively respond to Russia’s call for the extension of the New START, and carry out serious discussions with the Russian side on this,” he said.

Billingslea defended setting up the flags, saying “we configured the room for all three countries” in anticipation of China sending a delegation, then removed them to set up the room for bilateral talks.

Vladimir Isachenkov in Moscow, Lorne Cook in Brussels and Liu Zheng in Beijing contributed to this report.

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