LONDON (AP) – The next two days are “fairly critical” to resolving the dispute over a seized British navy crew, British Prime Minister Tony Blair said Tuesday, after Iran’s chief international negotiator offered a new approach to end the standoff with Tehran.

Mr. Blair told Scotland’s Real Radio that Ali Larijani’s suggestion of talks offered hope of an end to the crisis. “If they want to resolve this in a diplomatic way the door is open,” the prime minister said.

But if negotiations to win the quick release of the 15 sailors and marines stalled, Britain would “take an increasingly tougher position,” he said.

The navy crew was detained March 23 by naval units of the Iranian Revolutionary Guards while the Britons patrolled for smugglers near the mouth of the Shatt al-Arab, a waterway that long has been a disputed dividing line between Iraq and Iran.

Iran says the team was in Iranian waters. Britain insists it was in Iraqi waters working under a U.N. mandate.

Iran has previously demanded an apology from Britain as a condition for the sailors’ release.

Mr. Blair said Tuesday that Britain had two options in its approaches with Tehran.

“One is to try settle this by way of peaceful and calm negotiation to get our people back as quickly as possible,” he said. “The other is to make it clear that if that is not possible that we have to take an increasingly tougher position.”

On Monday, Larijani said that Iran sought “to solve the problem through proper diplomatic channels” and proposed having a delegation determine whether British forces had strayed into Iranian territory in the Persian Gulf. He did not say what sort of delegation he had in mind.

Mr. Larijani told Britain’s Channel 4 news Monday through an interpreter that Iranian officials “definitely believe that this issue can be resolved and there is no need for any trial.”