Russ­ian forces have tak­en four bor­der vil­lages in Ukraine’s north­east­ern Sumy re­gion, a lo­cal of­fi­cial said Tues­day, days af­ter Russ­ian Pres­i­dent Vladimir Putin said he had or­dered troops to es­tab­lish a buffer zone along the bor­der.

Sumy bor­ders Rus­sia’s Kursk re­gion, where a sur­prise Ukrain­ian in­cur­sion last year cap­tured a pock­et of land in the first oc­cu­pa­tion of Russ­ian ter­ri­to­ry since World War II. The long bor­der is vul­ner­a­ble to Ukrain­ian in­cur­sions, Putin said, and cre­at­ing a buffer zone could help Rus­sia pre­vent fur­ther cross-bor­der at­tacks there.

Mean­while, a Russ­ian bomb­ing cam­paign that had es­ca­lat­ed in re­cent days slowed overnight, with far few­er Russ­ian drones tar­get­ing Ukrain­ian towns and cities.

Moscow’s in­va­sion has shown no signs of stop­ping de­spite months of in­tense U.S.-led ef­forts to se­cure a cease­fire and get trac­tion for peace talks. Since Russ­ian and Ukrain­ian del­e­ga­tions met in Turkey on May 16 for their first di­rect talks in three years, a large pris­on­er ex­change has been the on­ly tan­gi­ble out­come, but ne­go­ti­a­tions have brought no sig­nif­i­cant break­through.

The U.S. spe­cial en­voy to Ukraine, Kei­th Kel­logg, said Putin has not yet de­liv­ered a promised mem­o­ran­dum that the Russ­ian leader told U.S. Pres­i­dent Don­ald Trump in a phone call on May 19 would out­line the frame­work for a pos­si­ble peace agree­ment.

The Krem­lin has al­so ruled out the Vat­i­can as a venue for ne­go­ti­a­tions, he said. “We would have liked to have it at the Vat­i­can and we were pret­ty set to do some­thing like that, but the Rus­sians didn’t want to go there … so I think Gene­va may be the next stop,” Kel­logg told the Fox News Chan­nel.

Turk­ish For­eign Min­is­ter Hakan Fi­dan said his coun­try al­so was ready to host an­oth­er round of peace talks.

Be­tween Fri­day and Sun­day, Rus­sia launched about 900 drones at Ukraine, of­fi­cials said, amid a spate of large-scale bom­bard­ments. On Sun­day night, Rus­sia launched its biggest drone at­tack of the 3-year-old war, fir­ing 355 drones.

From Mon­day to Tues­day, Rus­sia fired 60 drones at Ukraine, the Ukrain­ian air force said. Rus­sia’s De­fense Min­istry said its de­fens­es downed 99 Ukrain­ian drones overnight over sev­en Russ­ian re­gions.

The week­end surge in Russ­ian bom­bard­ments drew a re­buke from Trump, who said Putin had gone “crazy.” That com­ment brought a sharp Krem­lin re­ac­tion Mon­day, with spokesman Dmit­ry Peskov crit­i­ciz­ing ”emo­tion­al re­ac­tions” to events.

He took a milder tone Tues­day, hail­ing U.S. peace ef­forts and say­ing that “the Amer­i­cans and Pres­i­dent Trump have tak­en a quite bal­anced ap­proach.”

But Trump kept up the rhetor­i­cal pres­sure, say­ing in a so­cial me­dia post that Putin was “play­ing with fire!”

“What Vladimir Putin doesn’t re­al­ize is that if it weren’t for me, lots of re­al­ly bad things would have al­ready hap­pened to Rus­sia, and I mean RE­AL­LY BAD,” he said.

In Sumy, Russ­ian forces are try­ing to ad­vance deep­er af­ter cap­tur­ing vil­lages, said Oleh Hry­horov, head of the Sumy re­gion­al mil­i­tary ad­min­is­tra­tion.

Ukrain­ian forces are try­ing to hold the line, he said, adding that res­i­dents of the vil­lages were evac­u­at­ed ear­li­er, and there is no im­me­di­ate threat to civil­ians.

Putin vis­it­ed the Kursk re­gion last week for the first time since Moscow claimed last month that it drove Ukrain­ian forces out of the area where they cap­tured land last Au­gust. Kyiv of­fi­cials have de­nied the claim.

The long bor­der re­mains vul­ner­a­ble to Ukrain­ian in­cur­sions, Putin said. He said he told the Russ­ian mil­i­tary to cre­ate a “se­cu­ri­ty buffer zone” along the fron­tier but pro­vid­ed no pub­lic de­tails of where the pro­posed zone would be or how far it would stretch.

Putin said a year ago that a Russ­ian of­fen­sive at the time aimed to cre­ate a buffer zone in Ukraine’s north­east­ern Kharkiv re­gion. That could have helped pro­tect Rus­sia’s Bel­go­rod bor­der re­gion, where fre­quent Ukrain­ian at­tacks have em­bar­rassed the Krem­lin.

Davies re­port­ed from Man­ches­ter, Eng­land. Dar­lene Su­perville in Wash­ing­ton and Suzan Fras­er in Ankara, Turkey, con­tributed.

By KATIE MARIE DAVIES