Kabul, Afghanistan (CNN) -- U.N. Secretary-General Ban Ki-moon arrived in the Afghan capital Monday, less than a week after an attack on a guesthouse killed five U.N. workers and wounded nine others.
Ban met with President Hamid Karzai and former presidential candidate Abdullah Abdullah, the U.N. said in a statement.
On Sunday, Abdullah withdrew from a runoff election scheduled for this weekend, citing fears of fraud.
Ban was also meeting U.N. employees and officials, including Kai Eide, head of the United Nations Assistance Mission in Afghanistan.
The United Nations has said it is reviewing its security procedures in the aftermath of Wednesday's attack.
All nonessential staff have been evacuated from the country. The Taliban claimed responsibility for the attack.
International troop levels increased this year to provide security for the Afghan election in August, and the United States is considering deploying more troops.
CNN's Tommy Evans contributed to this report.