LONDON — Iran and North Korea have appointed high-level delegations to deepen cooperation between the two countries on nuclear weapons technology, according to diplomatic sources in Beijing.

The countries are keen to seal a deal before North Korea starts to close its Yongbyon reactor under the terms of an agreement with America and regional powers in February.

The February 13 accord was negotiated after North Korea conducted a successful test of a nuclear warhead at the end of last year. Following the international outcry that greeted the test, Pyongyang agreed to close the reactor in return for aid.

But the North Koreans missed the weekend’s deadline to start shutting down the reactor, claiming that America was refusing to release about $30 million of North Korean funds frozen in bank accounts in Macau.

The U.S. State Department has demanded that North Korea should “immediately” invite the International Atomic Energy Agency to begin sealing the facility.

South Korea said yesterday that it was considering delaying rice aid to North Korea because of Pyongyang’s failure to comply with the agreement.

Iran has taken advantage of the delay to intensify attempts to negotiate a deal that would give Tehran access to the nuclear expertise North Korea acquired during last year’s atom bomb test.

Iranian scientists have already been invited to Pyongyang to study data collected from the test. Beijing-based diplomats responsible for monitoring North Korea say that Iran is now keen to negotiate a deal that would deepen the level of nuclear cooperation.

Although, under the terms of the February agreement, North Korea has agreed to shut the Yongbyon reactor — which provided the fissile material for the nuclear test — the agreement puts no limits on North Korea to export the expertise it acquired from the test.

“As the agreement currently stands, there are no restrictions on the proliferation of nuclear technology North Korea acquired last year,” said a well-placed diplomat. “Iran is desperate to take advantage of this loophole to buy Pyongyang’s expertise on building nuclear weapons.”

The Iranian delegation handling the negotiations with North Korea report directly to Reza Aghazadeh, the country’s vice president and the head of the Atomic Energy Organization of Iran, who has overall responsibility for the program.