Kabul, Afghanistan ? The United Nations has encouraged some nonessential staff to leave Afghanistan amid security concerns ahead of Sept. 18 elections, and the government warned aid workers Sunday that they are likely targets after a string of assaults on foreigners.

The insurgents, meanwhile, launched a fresh spate of guerrilla-style strikes this weekend, sparking fierce battles that killed a district police chief, seven officers, an election candidate and three others, officials said.

More than 1,100 people have been killed in the past six months, and U.S. military commanders believe the violence may worsen as rebels step up attacks with legislative elections just two weeks away, the next key step toward democracy after a quarter century of fighting.

U.N. spokesman Adrian Edwards told The Associated Press that some of the world body’s agencies had urged some employees to take vacation during the elections because of fears of violence, though he noted that the official U.N. alert level had not changed.

“The United Nations continues to monitor the security situation,” he said.

Emma Sutcliffe, a U.N. Development Program communications associate, said “We have been encouraged to take R and R (rest and recreation), but it’s not mandatory.”

“For those who remain behind, there’ll be minimal movement,” she said.

Other U.N. agencies though, including the World Food Program and the U.N. High Commissioner for Refugees, said they had not increased their security precautions.

U.S. Embassy spokesman Lou Fintor said the security status at the heavily guarded mission had not changed but stressed the threat situation was constantly being monitored.

News that some U.N. staff were being encouraged to leave came after Interior Ministry spokesman Latfullah Mashal warned of more attacks.

“They (militants) focus on soft targets, attacking candidates, burning schools, aid workers,” he told AP. “But the security workers have also taken necessary measures to provide needed security.”

He said he was optimistic that the elections would be successful even though “al-Qaida and the Taliban will try their best to disrupt peace and stability.”