Six world powers and Iran appear to be still a long way from being able to overcome major differences and to agree to a deal over Tehran's nuclear program by a self-declared deadline of November 24.
Western news agencies quote a U.S. State Department official at the talks in Vienna as saying privately on November 22 that Washington still hopes to get a nuclear deal with Iran by the deadline but is also examining "options."
"The focus of discussions remains on an agreement, but we are discussing both internally and with our partners a range of options for the best path forward," the State Department official said.
The comment comes after U.S. Secretary of State John Kerry said earlier in the day that there are still serious gaps in the positions of the six powers and Iran.
"We're working hard," Kerry said ahead of a meeting with German Foreign Minister Frank-Walter Steinmeier in Vienna on November 22.
"We hope we're making careful progress, but we have big gaps, we still have some serious gaps, which we're working to close," Kerry said.
Steinmeier joined the talks in Vienna on November 22 in a new sign of accelerating efforts to get a deal by November 24.
He said on arriving that despite huge gaps in the negotiations, "we have never been closer in more than 10 years."
He added, "If Iran is ready to take this opportunity then movement is possible ... Whether we can get a result is right now completely open."
Kerry also met with Iranian Foreign Minister Mohammad Javad Zarif and European Union envoy Catherine Ashton on November 22.
Kerry and Zarif had earlier taken part in a marathon session overnight in an effort to break the deadlock in reaching a deal but without any reported success.
Meanwhile, Russia's Foreign Ministry said on November 22 that Foreign Minister Sergei Lavrov had changed his schedule, postponing meetings with African envoys scheduled for November 24 in Moscow.
The ministry had said earlier that Lavrov and Kerry agreed in a telephone conversation that "additional efforts" were needed to reach a deal by November 24.
Deputy Foreign Minister Sergei Ryabkov, who is in Vienna, indicated that Lavrov may also travel to there over the weekend, but "no final decision has been made yet."
Kerry and Zarif had stayed overnight in Vienna in a bid to break the deadlock in the year-long round of negotiations, despite earlier reports that the two intended to leave the Austrian capital.
Ryabkov said early on November 22 that the negotiators cannot afford to lose a single hour -- not even to take flights back to their capitals for consultations.
He told journalists in Vienna that the fact that Kerry and Zarif have stayed in Vienna "signals that the work may be crowned with success" -- but only if each side meets the other "halfway."
A group of six world powers wants Iran to curb its nuclear program in return for lifting sanctions.
White House spokesman Eric Schultz said the negotiators were "working furiously" to try to meet the deadline.
But the White House acknowledged as the two began their overnight meeting that "serious gaps" remained in their deadlocked talks.
Before the marathon overnight session began, Zarif said that there had been "important discussions" earlier on November 21, "but no significant proposition worth returning to Tehran with."
Kerry initially had planned to travel to Paris to consult with European officials in the P5+1 group of world powers, consisting of the five permanent members of the UN Security Council -- the United States, Russia, China, the United Kingdom, and France -- plus Germany .
Washington has said that it does not want to see the self-declared November 24 deadline extended.
U.S. State Department Spokesman Jeff Rathke told reporters in Washington on November 21: “We’re not talking about an extension [of the November 24 deadline] with the Iranians, we’re not focused on that.”
But a European source close to the negotiations said on November 22 that the parties have made "no significant progress" in the talks and the "Iranians will have to move in a substantial way" in order to reach a full agreement.
"The goal is to reach a precise agreement... At this stage the idea that we can wrap up the whole thing [by November 24] is physically impossible," the source told journalists on condition of anonymity.
"Even if we reach a political agreement, the technical annexes will not be ready," the source added.
Iran and the P5+1 forged an interim agreement a year ago and are now trying to finalize a permanent, comprehensive deal that eliminates concerns Tehran could build a nuclear weapon and which gives Iran relief from UN and Western sanctions.
A major sticking point has been over Iran's refusal to substantially cut the output of centrifuges that can enrich uranium to levels high enough to be used for nuclear weapons.
Iran insists its nuclear program is only being used for peaceful civilian purposes such as power generation and medical research.