As President Obama announced sanctions against Russia on Monday, a group of Russian officials arrived in San Francisco for a surprise inspection of the U.S. strategic nuclear arsenal.

The inspections, part of a process agreed to under the 2010 New START weapons reduction treaty, signaled business as usual in at least one area of bilateral cooperation.

The treaty is far from the only arms-control investment between the two countries. Russia and the United States have cooperated on efforts to keep nuclear materials out of terrorist hands, they are jointly negotiating limitations on Iran’s nuclear program, and they have joined in the effort to destroy Syria’s chemical weapons arsenal.

So far, all of those efforts have been off-limits in the dispute over Ukraine that has sent U.S.-Russia relations into a steep, downward spiral, and have proceeded without interruption.

Administration officials have been quick to emphasize that they would like to keep it that way and have repeatedly said they believe Russia feels the same way.

Russia is key to the nonproliferation agenda, which has been Obama’s signature foreign policy initiative. Asked Friday whether Moscow intends to remain cooperative, national security adviser Susan E. Rice said, “We haven’t seen any evidence to the contrary.”

But the Russian approach to international comity and norms has been uneven. Late this week, even as it officially annexed Crimea while the rest of the world cried foul, Moscow facilitated Ukrainian overflights of Russian troop emplacements on their shared border, under the 1992 Open Skies Treaty that is part of the world’s intricate system of security arrangements.

Under New START, Russia and the United States each agreed to reduce their strategic warheads to 1,550 by 2018. Russia shunned an offer by Obama last year to negotiate further reductions, in part over its objections to U.S. missile defense plans in Eastern Europe, but it continues to abide by provisions of the treaty.

Its provisions include 18 surprise inspections by both sides each year. The teams do not have to say which military installation they want to visit or reveal reveal what they want to see until they arrive. The surprise element, a senior administration official said, ensures that “there’s no chance to stash anything away or move it out of the line of sight. That’s a very important part of the treaty.”

The most recent U.S. inspection in Russia took place during the last week of February, just as the administration said that Russian troops were beginning to pour into Crimea.

The treaty has a clause that allows either side to withdraw, and the senior official, who spoke on the condition of anonymity about the increasingly sensitive relationship, said that “if the Russians at some point decided they wanted to exercise” that right, they could do so.

“But I hope they would think very long and hard about that,” the official said.

Next week, Obama will travel to the Netherlands for a summit on nuclear security, the third in a series he initiated during his first year in office in a major speech that called for international efforts to prevent nuclear terrorism.

Although Russian President Vladi­mir Putin will not attend, a Russian delegation will be headed by Foreign Minister Sergei Lavrov. One key to the summit’s success will be the ability of all involved to separate its agenda from the series of international meetings on the Ukraine crisis that Obama will attend immediately afterward in Belgium, from which the Russians pointedly will be excluded.

“We haven’t seen any evidence so far” that Russia will use the summit to express unhappiness over Ukraine, the senior official said. “As far as I can tell, all the materials, the final statement, have been well-agreed” on by all participants, the official said, and “there’s been no pushback” from Moscow.

The extent to which Russia is willing to separate Ukraine from other issues in which the United States and its partners have major equities arose this week at the end of the latest round of talks in Vienna over Iran’s nuclear program.

Russia is one of the six nations — with the United States, Britain, France, China and Germany — that is negotiating with Iran to ensure it has no nuclear weapons capability. In a statement Wednesday at the end of the latest round, Russian Deputy Foreign Minister Sergei Ryabkov, his country’s chief envoy to the talks, warned that Moscow might use them to take “retaliatory measures” against Western sanctions.

Noting that Russia considered “reunification” with Crimea more important than the Iran negotiations, Ryabkov said, “We wouldn’t like to use these talks as an element of the game of raising the stakes, taking into account the sentiments in some European capitals, Brussels and Washington,” according to Russia’s Interfax news agency.

But the issue seemed to disappear just as quickly as it the administration’s anxiety rose, and there has been no further mention of the matter from Russia.

“We saw no change” in the posture of negotiators “related to the situation in Ukraine,” said another senior administration official who briefed reporters Thursday on the new round of U.S. sanctions on Russia. “To date, things have continued apace in terms of how we’ve worked with Russia.”

“The second point I’d make,” the official said, is that whatever its differences with the West, “Russia has no interest in nuclear proliferation or an escalation of the situation in the Persian Gulf.”

In its own coverage of the talks, Iran chose to emphasize different comments by Ryabkov, who also said the negotiations had “progressed quite well, the atmosphere is very good, and the work is business-like and result oriented.”

Iranian Foreign Minister Mohammad Javad Zarif, agreed that, while there was a long way to go, the talks showed promising signs, according to Iran’s Fars News Agency.

On the issue of Syria, U.S.-Russia-sponsored peace talks are at a standstill and Moscow has shown no sign of lessening its support for Syrian President Bashar al-Assad. Barely a month ago, a U.S.-Russia initiative to remove Syrian chemical weapons appeared to be bogged down and unlikely to meet its goal of complete removal and destruction by the end of June.

In one of its first responses to Russian aggression in Crimea, NATO announced last month that it was canceling what would have been the first NATO-Russia joint operation — a Russian naval escort for the U.S. ship on which Syrian chemical weapons are to be destroyed at sea.

Nonetheless, the removal effort has picked up substantially. This week, the Organization for the Prohibition of Chemical Weapons announced that nearly half of Syria’s chemical stockpiles were now out of the country and on their way to destruction.

“Russia is deeply invested in that project,” the administration official who briefed reporters Thursday said. “We’re confident that, given Russia’s own interest in seeing these weapons destroyed, we will continue with that effort.”