US Deputy Secretary of State Williams Burns will join talks between Iran and the P5+1 in Vienna on Monday, a US official told Al-Monitor.

Burns was seen by Al-Monitor on the plane Sunday traveling with the US delegation, led by Undersecretary Wendy Sherman, to Vienna from Washington. He and Sherman are expected to meet Monday with Iranian and European Union negotiators. Sherman will stay on for nuclear talks between Iran and the P5+1 expected to go til Friday, as efforts intensify to reach a final nuclear accord by July 20.

“We’re at a critical point in these negotiations, and we’re going to work as hard as we possibly can to see if we can get to an agreement here,” a senior U.S. Administration official told Al-Monitor Monday. “Deputy Burns will be joining for meetings on the 16th, including an expected trilateral with Iran and the EU.”

“We’ve always said our diplomatic efforts would continue to intensify, and they have,” the US official said. “This is another example of that effort. And we’ve been clear that various members of our negotiating team – especially the Deputy, given his history working on this issue with the Iranians – will participate in various meetings throughout this process.”