Britain’s foreign secretary, Philip Hammond, said on Wednesday that a nuclear deal with Iran is unlikely to be completed by a deadline next Monday but there may be enough progress to warrant extending the talks.

“I’m not optimistic that we can get everything done by Monday,” Hammond told reporters during a visit to the Latvian capital, Riga, according to The Guardian.

“But I think if we make some significant movement we may be able to find a way of extending the deadline to allow us to get to the final deal if we’re making good progress in the right direction,” he added.

The foreign secretary said Iranian negotiators would have to show “considerable further flexibility” over the next four days to get a deal.

Iran and six world powers have been engaged in talks to turn an interim deal signed last year into a permanent one.

However, despite assurances it is confident of reaching a deal by the November 24 deadline, Iran has been toughening its stance in recent weeks. Iran’s chief negotiator, Abbas Araqchi, recently said he sees no prospect for a deal unless the other side abandons its “illogical excessive demands”.

A senior Iranian official followed those comments by declaring that Iran will demand that all Western sanctions be lifted as part of a final deal, rejecting an American proposal of a gradual lifting of sanctions.

The official position of both the United States and Iran, the two countries at the center of the talks, is that an extension to the November 24 deadline is not under discussion.

The cut-off date was agreed as part of an interim deal a year ago but as it approaches with no sign of a breakthrough on the outstanding issues, an extension is looking increasingly likely.

 “We do very much want to see a deal done with Iran, but we don’t want to do a bad deal. Better no deal than a bad deal,” Hammond said.

“The right deal with Iran has to be one which gives us the assurance we need that Iran’s program is exclusively targeted at civil nuclear use, has no military dimension at all and where Iran’s enriched capacity is limited to a level which does not present any military threat,” he added.