WASHINGTON, December 24 - The US is contemplating incursions into Syrian territory in an attempt to kill or capture Iraqi Ba'athists who, it believes, are directing at least part of the attacks against US targets in Iraq, a senior administration official told The Jerusalem Post.

The official said that fresh sanctions are likely to be implemented, but added that the US needs to be more "aggressive" after Tuesday's deadly attack on a US base in Mosul. The comment suggested that the US believes the attack on the mess tent, in which 22 people were killed, may have been coordinated from inside Syrian territory.

"I think the sanctions are one thing. But I think the other thing [the Syrians] have got to start worrying about is whether we would take cross-border military action in hot pursuit or something like that. In other words, nothing like full-scale military hostilities. But when you're being attacked from safe havens across the border – we've been through this a lot of times before – we're just not going to sit there.

"You get a tragedy [like the attack in Mosul] and it reminds people that it is still a very serious problem. If I were Syria, I'd be worried," the senior administration official said.

Another US official said that sentiment reflects a "growing level of frustration" in Washington at Syria's reluctance to detain Ba'athists and others who are organizing attacks from Syrian territory. The official cautioned, however, that whether to take cross-border military action is still a matter of discussion within the administration and that a military incursion is still "premature."

The senior official said US anger increased substantially after a prolonged incursion into Fallujah last month, which revealed "how much of the insurgency is now being directed through Syria." The US has not publicly detailed the evidence it has regarding the extent to which attacks are being organized from within Syria. But a report in The Times of London on Thursday suggested not only that Syria is becoming a base for Iraqis to operate, but that Syrian officials are themselves involved.

The newspaper said Iraq had confronted Syria with evidence that included photographs of senior Syrian officials taken from Iraqi fighters captured during the Fallujah offensive. It also said US marines in Fallujah found a hand-held global-positioning system receiver with waypoints originating in western Syria and the names of four Syrians in a list of 27 fighters contained in a ledger.

On Sunday, the Post reported that the US had provided Syria with a list of people it would like to see detained but that Syrian authorities have so far been unresponsive. The Post quoted a senior government official predicting a confrontation with Syria "unless the Syrians reverse their policy." US forces already operate along the Syrian border with Iraq, conducting air and mobile patrols.

This week, US President George W. Bush warned of possible new sanctions on Syria. "We have tools at our disposal, a variety of tools ranging from diplomatic tools to economic pressure. Nothing's taken off the table," he said.

And in an interview with a Lebanese newspaper, Deputy Secretary of State Richard Armitage echoed the threat of new sanctions. In particular, Armitage said Washington wanted action taken against fugitive officials of the ousted regime, who remained at liberty in Syria and who "seem to us to be responsible for funding anti-US attacks in Iraq." "We want them to turn off this faucet," said Armitage, according to the paper's Arabic translation of his remarks.

Syria says it is doing all it can to prevent insurgents from crossing the Syrian border into Iraq and insists it would need more help to confront the problem. It also says it is being unfairly singled out whereas Ba'athists and others feeding the insurgency are hiding in other countries in the region.