SAN DIEGO >>U.S. Homeland Security Secretary John Kelly told law enforcement officials on a tour of nation’s border with Mexico today that he couldn’t define a sanctuary city, which President Donald Trump has targeted for withdrawal of federal funding for refusing to cooperate with immigration authorities.

Trump’s executive order on immigration last month says a “sanctuary jurisdiction” defies federal law by shielding people in the country illegally and that they have caused “immeasurable harm to the American people and to the very fabric of our Republic.” While sanctuary cities are broadly understood to mean a refusal to cooperate with the federal government on immigration enforcement, a precise definition has eluded many, including in law enforcement.

“I don’t have a clue,” Kelly told San Diego Police Chief Shelley Zimmerman when she asked for a definition.

The blunt-spoken, retired four-star general went on to say it was inconceivable why any jurisdiction wouldn’t want criminals removed from their communities. “I’m stunned when people say, ‘Well, we’re not going to cooperate with you even in the event of convicted criminals,” he said.

Kelly said it would be difficult to justify immigration enforcement grants to cities that refuse to cooperate.

“I promise you we’ll work with you and will make no Draconian moves until I fully understand what a given locale might be doing or not doing,” he told Zimmerman and other local police chiefs and sheriffs.

Kelly spoke near the end of a two-day tour of the border in Arizona and California. In San Diego, he joined agents on two house visits to deport people in the country illegally and toured a cross-border drug tunnel. Last week he toured the border in south Texas.

The secretary said he got “an earful” of suggestions from his employees on where to extend a border wall with Mexico, which currently covers about 700 miles of the 2,000-mile international divide.

“I’ll take that on board, we’ll bring it back to Washington, put in the blender and come up with a solution,” he told federal, state and local law enforcement officials at San Diego’s San Ysidro port of entry, the nation’s busiest border crossing.

On Tuesday, Kelly told lawmakers that he would like to see wall construction “well underway” within two years, but he held open the possibility that it wouldn’t extend to areas where there are natural physical barriers.

San Diego, which has one of the most fortified stretches of border, is often cited as an example of how walls can slow illegal crossings, but critics say fencing only forced people to more remote areas, particularly in Arizona, where many have died in extreme heat.

Kelly later told reporters that he worried about a federal appeals court’s refusal to reinstate Trump’s ban on travelers from seven predominantly Muslim countries. He said vetting practices in those countries “are loose at best” and that the countries include failing or faltering states.

“I am concerned in that we are unable to vet these folks who are coming here in a more meaningful way,” he said.

Asked about reports from advocacy groups that U.S. Immigration and Customs Enforcement agents did a large roundup of people in the country illegally in Southern California and made arrests elsewhere, Kelly said authorities are executing the law. He didn’t specifically address the reports but rejected the term ‘roundup’ and said officials cannot ignore federal laws. He said Congress should change the law if it sees fit.

At the meeting with law enforcement officials, San Diego County Sheriff Bill Gore sought help for legal authority to hold criminals in the country illegally after they finish their sentences, giving ICE authorities more time to pick them up at county jails. Kelly said he didn’t know if that was possible but would do so if he could.