Washington ? A senior Bush administration official on Tuesday accused Syria of allowing Islamic militants to cross into Iraq to kill U.S. soldiers and said the Syrian government was pursuing a program to develop weapons of mass destruction.

Undersecretary of State John Bolton said the Bush administration was trying to resolve its differences with Syria through diplomacy. But he left open the possibility of tougher action.

“Our preference is to solve these problems by peaceful and diplomatic means, but the president has also been clear that we are not taking any options off the table,” said Bolton, who oversees U.S. efforts to prevent the global spread of nuclear, chemical and biological arms.

“We have seen Syria take a series of hostile actions toward coalition forces in Iraq,” Bolton told the Middle East subcommittee of the House International Affairs Committee. “Syria permitted volunteers to pass into Iraq to attack and kill our service members during the war and is still doing so.”

Rep. Ileana Ros-Lehtinen, R-Fla., who is chairwoman the subcommittee, is sponsoring a bill that has wide bipartisan support to use economic and diplomatic sanctions against Syria if it does not end its support for terrorist groups such as Hezbollah and continues to stockpile chemical weapons.

The administration has not taken a position on the legislation, but Secretary of State Colin Powell said Monday in Kuwait that Syria was not cooperating with U.S. requests and faced the threat of a sanctions bill if it did not change.

In the public portion of his testimony, Bolton said that Syria has stockpiles of the nerve agent sarin.