U.S. Secretary of Defense Robert Gates has expressed discontent over the results of the six-way nuclear talks.

In a prepared statement to the Senate Armed Services Committee, Gates said the six-nation nuclear talks have been essential in producing some forward momentum, especially with respect to North Korea’s plutonium production.

However, he added that he doesn’t think anyone can claim to be completely satisfied with the results so far.

He said the nuclear negotiations do offer a way to curtail and hopefully eliminate Pyongyang’s capacity to produce more plutonium or to enrich uranium, while at the same time reducing the likelihood of proliferation.

Gates, who is the only Republican Cabinet member whom President Barack Obama asked to stay on, stressed that Washington’s goal remains denuclearization. However, he said it remains to be seen whether North Korea is willing to give up its nuclear ambitions entirely.

Meanwhile, Gates told the Senate panel that Afghanistan should be Washington’s top overseas military priority, saying the U.S. is considering delivering three additional combat brigades to the war-torn nation before this summer.