UNITED NATIONS - Iranian Foreign Minister Mohammad Javad Zarif will meet Thursday with Secretary of State John Kerry and representative of five other world powers, in what will be the highest-level face-to-face meeting between diplomats from Tehran and Washington since the 1979 Iranian revolution. The two will come together at the U.N. in a session of the so-called P5 Plus One diplomatic group, which has been meeting for seven years to try to negotiate curbs on Iran's nuclear program. The meeting was announced by Catherine Ashton, the European Union's foreign policy chief. U.S. and Iranian officials have been hinting for weeks that senior officials might meet at this week's United Nations General Assembly to begin an intensified round of negotiations, possibly including one-on-one talks between the two countries. White House officials have signaled that President Obama might even meet informally on the sidelines of the gathering with Iran's new president, Hassan Rouhani. Ashton's announcement marked the first concrete step toward intensified contacts. Ashton did not suggest that the meeting would provide for an in-depth exploration of the nuclear issues, but said it would allow for a "short discussion." She also disclosed that she and other EU officials would meet, on behalf of the P5 Plus One, with Zarif and other Iranian officials in Geneva in October. Western diplomats have been predicting for months that there would be a P5 Plus One meeting this fall to probe whether Rouhani, a relative moderate, might be more open to compromise than his predecessor, Mahmoud Ahmadinejad. But the group negotiations, which have been stalemated for years, have generated less excitement in recent weeks than the possibility of bilateral negotiations between Iran and the United States. If Obama and Rouhani do meet, they would probably do so Tuesday at the United Nations. The two top leaders could meet briefly to signal their desire for face-to-face talks, and deputize lower level officials to begin planning the meetings. Jen Psaki, a State Department spokeswoman, said Kerry "welcomes the foreign minister's commitment to a substantive response and to his agreement to meeting in the short term" to meet with the P5 Plus One. We remain ready to work with Iran should the Rouhani administration choose to engage seriously. The six powers have indicated in recent weeks that they didn't intend to present Iran a new offer, but wanted to hear Iran's response to the plan that group put down last spring in Kazakhstan. [For the Record, 11:10 a.m. 23: A previous version of this post said Catherine Ashton, the European Union's foreign policy chief, also disclosed that there would be meeting of the P5 Plus One in October in Geneva. Ashton said at that meeting that she and other EU officials will meet, on behalf of the P5 Plus One, with Zarif and other Iranian officials.]