VIENNA, July 13 -- Foreign ministers and deputy ministers from six world powers involved in the Iranian nuclear talks on Sunday met again in Vienna, Austria, but didn't make progress in reaching a comprehensive solution for the decade-long dispute.

As the time is running out, there are still significant gaps between Iran and the P5+1 nations on some key issues, especially Iran's uranium enrichment program. Before Sunday's meeting, Iran and the five permanent members of the United Nations Security Council -- the United States, Britain, France, Russia and China -- plus Germany, were engaged in one-week intensive negotiations in Vienna.

"There has been no breakthrough in these talks today," British Foreign Secretary William Hague told reporters after the talks, admitting there is still significant gaps in uranium enrichment issue.

Hague didn't want to focus on the extension of the Geneva deal given there is still hope to reach the comprehensive agreement by the deadline on July 20.

"That (the extension of the Geneva deal) will have to be discussed If it becomes clear that no other progress can be made," said Hague, urging Iran to be "more realistic" about what is necessary in order to reach agreement on those issues earlier before the meeting.

Under the interim deal agreed in Geneva last November, Iran agreed to suspend some sensitive nuclear activities in exchange of limited sanction relief in a duration of six moths to buy time for the diplomatic effort to resolve the nuke issue.

The six world powers are now working with Iran in Vienna to find a comprehensive solution to put an end to Tehran's long-term controversial nuclear program. The West wants Iran to significantly scale back its nuclear program to address its concern of proliferation risk, while Iran insists its nuclear right is inalienable.

Earlier in the day, U.S. Secretary of State John Kerry also said there still exist major differences between Iran and the six world major countries attending the talks.

"And obviously we have some very significant gaps still," said Kerry, who arrived in Vienna Sunday to join the talks. "So we need to see if we can make some progress."

"It is vital to make certain that Iran is not going to develop a nuclear weapon and that their program is peaceful. That's what we're here to try to achieve. And I hope we can make some progress on it," Kerry said.

The meeting of the foreign ministers also aimed at assessing the situation of the negotiations as the deadline looms.

Chinese vice foreign minister Li Baodong said the talks now are in the critical moments and should move forward.

Since the significant gaps are not bridged in the talks, and time is running short, experts believe that the negotiation could probably need more time to reach a final deal.