By Jack Kim

SEOUL (Reuters) - A team led by a U.S. State Department nuclear envoy entered North Korea on Thursday to persuade Pyongyang to declare its nuclear activities as called for in a six-country disarmament deal, an official said.

U.S. envoy Sung Kim led a similar delegation to the secretive state about two weeks ago, pressing for an inventory of its fissile material and nuclear weaponry and for answers to U.S. charges that it enriched uranium for weapons and transferred technology to Syria.

Kim crossed into the North by land over the heavily fortified Demilitarized Zone border, a U.S. embassy official in Seoul said.

North Korea failed to disclose the list of its nuclear activities by a December 31, 2007 deadline set in the disarmament deal it reached with China, Japan, Russia, South Korea and the United States.

If it makes the nuclear declaration, Washington will start to take North Korea off its terrorism blacklist and lift a trading ban.

Kim's return visit reflects an accelerated U.S. effort to secure the declaration, analysts have said.