UNITED NATIONS -- U.S. Ambassador Susan Rice says the U.N. Security Council is studying how to respond to revelations about a new uranium enrichment plant in North Korea and the country's shelling of a populated island in neighboring South Korea.

Rice spoke Monday after the powerful 15-member group held routine consultations on U.N. sanctions against communist-led North Korea.

She says the council's concerns about North Korea's nuclear activities have been heightened by its attack last week on Yongbyon, an island under U.N. command and administered by South Korea. Two South Korean marines and two civilians were killed in the shelling.