A week after Mayor Bill de Blasio trumpeted the success of the NYPD's summer anti-crime initiative, new police data released Monday showed that a burst of shootings and homicides has reversed weeks of improvements.

Police chalked up some of the killings and gunfire to a weekend with some of the year's hottest weather, continuing gang violence and chance confrontations such as a Bronx post-Ramadan party Sunday where six people were shot and wounded.

For the year through Sunday, NYPD data showed the city recorded 186 homicides compared with 169 in the same period a year ago, or an increase of just over 10 percent. Shooting incidents totaled 622 compared with 610 in 2014 or an increase of 2 percent. Those numbers were the first time the percentages significantly increased since the summer began.

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"It was a tough weekend," said Deputy Commissioner Stephen Davis, chief spokesman for the NYPD.

"This was the hottest weekend of the year," he said, adding that the weather sets the tone for more people to stay out, party and become vulnerable to trouble, sometimes by chance.

Sunday in the Morris Heights area of the Bronx, six people were shot and wounded after a small group of inappropriately dressed people crashed a post-Ramadan party, causing a dispute, Davis said.

A search of the recent shootings and homicides revealed that the majority of them involved either drugs or gang disputes, a common theme the NYPD has found throughout the year, Davis said.

In response to an earlier rise this year in homicides and shootings, the NYPD accelerated by one month the start of its Summer All Out program, in which 330 desk duty cops were put on the beat in 10 high-crime precincts and four public housing areas.

Last week to extol the benefits of the program, Police Commissioner William Bratton and de Blasio went to the 47th Precinct in the Williamsbridge area of the Bronx to report that the summer initiative had reduced shootings and murders there and in some other precincts. DeBlasio also praised the NYPD's efforts to forge closer ties between the precincts and communities.

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But after the weekend, the latest spate of shootings had skewed the positive results in the Summer All Out precincts. Overall this year through Sunday, the initiative's 10 precincts showed a 133 percent increase in shooting incidents over the previous week and a 75 percent increase over the same week a year ago.

Seven of the Summer All Out precincts showed increases in shootings last week over the prior week. Two precincts, including the 47th, showed no change while one, the 73rd Precinct in East New York, Brooklyn, showed a decline.

Davis said that the NYPD will only know about the effectiveness of the Summer All Out initiative when it ends Oct. 1.