U.S. Secretary of State Marco Rubio meets the press after the NATO Foreign Ministers' meeting in Helsingborg, Sweden, Friday. Foreign ministers of the 32 NATO member states gathered in the Swedish city to finalise preparations for the upcoming Ankara Summit. AFP-Yonhap

DUBAI/HELSINGBORG, Sweden — The United States has seen some progress towards a deal with Iran but more work is required, Secretary of State Marco Rubio said Friday, while Iran's foreign ministry spokesman said the two sides' differences were deep and significant.

Intensifying diplomacy to end the conflict, Pakistan's military chief arrived in Tehran, Friday to press on with mediation efforts, and Iranian media reported that Iran's foreign minister and Pakistan's interior minister had met there.

Qatar also sent a negotiating team to the Iranian capital to try to resolve the sides' main differences, six weeks into a fragile ceasefire.

While some gaps have been narrowed, there are still sticking points over Iran's enriched uranium and control over the Strait of Hormuz, whose closure since the start of the war has triggered a global energy crisis.