New York ? Years after a six-month deadline passed, dozens of nations, including uranium producers, remain potential weak links in the global defense against nuclear terrorism, ignoring a U.N. mandate on laws and controls to foil this ultimate threat.

A man enters a tunnel dug with shovels April 10, 2004, in the Shinkolobwe cobalt mine in the Democratic Republic of Congo. U.N. Security Council Resolution 1540 of 2004 obligates governments to give a full accounting of their nuclear materials, but as President Barack Obama is host to a summit on nuclear security April 12-13 in Washington, many states have fallen short of the reporting deadline, including Congo, the source of the uranium for the first atomic bomb.

Niger, a major uranium exporter, and the Democratic Republic of the Congo, the source of the uranium for the first atomic bomb, are among the states falling short in complying with Security Council Resolution 1540, a key tool in efforts to block nuclear proliferation.

Uncontrolled freelance mining in the Congo has long worried international authorities that the raw material for a bomb might fall into the wrong hands.

U.S. President Barack Obama, who calls nuclear terrorism “the most immediate and extreme threat to global security,” plays host to a summit on nuclear security April 12-13 in Washington, where implementation of Resolution 1540 will be high on the agenda.

Twenty-nine nations have failed to report they have taken action on nuclear security as required by the 2004 resolution. Among the more than 160 governments that have reported, the information supplied is often sketchy.

Resolution 1540, which set a reporting deadline of October 2004, “imposes strict reporting requirements on states, but few have fully met them,” the International Commission on Nonproliferation and Nuclear Disarmament, a prestigious study group, concluded in its final report last December.

Mexican U.N. Ambassador Claude Heller, chairman of the U.N. committee monitoring 1540’s implementation, said he plans a series of meetings with noncompliant states to urge cooperation, and he sees Obama’s summit as a chance to “send a strong message” about the U.N. mandate’s importance.

“It is a legally binding regime that was adopted by the Security Council,” Heller told The Associated Press. “It is not up to governments to say yes we will report or not.”

Resolution 1540, promoted by the U.S. in the aftermath of the 9/11 terror attacks and the 2004 uncovering of the Pakistan-based A.Q. Khan nuclear smuggling network, is the only global legal instrument designed to disrupt links between terrorists and nuclear technology. Unlike treaties, applicable only to states that ratify them, this U.N. mandate obligated all nations.

It required governments to “adopt and enforce appropriate effective laws which prohibit any non-State actor,” such as terrorists, from making or possessing nuclear, chemical or biological weapons, their delivery systems or related material. Governments must establish “effective” border and export controls and physical protection for sensitive materials and sites.

An AP review of filings found vast differences in reporting. The U.S. and other industrialized nations filed reports of up to 30,000 words detailing relevant laws and how they are enforced, while other, smaller countries submitted reports of just a few hundred words noting — irrelevantly — the nonproliferation treaties to which they subscribe or, in Uganda’s case, requesting financial aid to carry out 1540’s obligations.

In its own review issued in January, Heller’s committee cited major gaps in reporting on whether activities related to weapons of mass destruction were criminalized, on whether laws are enforced, on establishing lists of controlled items, and on restricting access to sensitive materials.

Almost all the non-reporting states are in Africa, including uranium producers Zambia, Malawi and the Central African Republic.