WASHINGTON (AP) — President Donald Trump called Friday on Mexico to block MS-13 gang members from traveling through their country on the way to the U.S.

In a tweet, Trump said that gang members are being removed "by the thousands" by federal law enforcement agents, "but these killers come back in from El Salvador, and through Mexico, like water."

Trump accused El Salvador of just paying lip service to combatting the violent international gang based there and said Mexico "must help MORE with this problem." He added: "We need The Wall!"

The Friday morning tweet comes a day after Trump suggested he may pull the U.S. Immigration and Customs Enforcement agency out of California to protest so-called "sanctuary" jurisdictions, which the administration claims are a magnet for immigrants who commit crimes.

Energy Secretary Rick Perry said Friday that the threat merely a negotiating tactic.

"The President is a first-rate negotiator," he told Fox & Friends Friday morning, "and I will suggest to you that that is what is going on."

Perry says Trump is "clearly" sending messages not just to California, "but also to Congress."

Trump Thursday said his administration is making strides against the MS-13 gang but has been "getting no help from the state of California."