BAGHDAD — Iraqi security forces battled insurgents targeting the country's main oil refinery and claimed to regain partial control of a city near the Syrian border today, trying to blunt a weeklong offensive by militants who diplomats fear may have abducted some 100 foreign workers.

The campaign by the al-Qaida-inspired Islamic State of Iraq and the Levant has raised the specter of the sectarian warfare that nearly tore the country apart in 2006 and 2007 and the doubts that followed the 2003 U.S.-led invasion now haunt those trying to decide how to respond.

President Barack Obama was to brief lawmakers today at the White House on what options the U.S. could take.

Iraqi Prime Minister Nouri al-Maliki, meanwhile, struck an optimistic tone after soldiers abandoned their posts in the wake of the initial offensive, promising his nation would teach the attackers a “lesson.”

KIEV, Ukraine — The Ukrainian president today announced a plan to end the fighting in eastern Ukraine, promising a unilateral cease-fire after discussions with the Russian and German leaders, a potential major development to bring peace to the country.Petro Poroshenko's plan would offer pro-Russian insurgents in the eastern provinces that form the nation's industrial heartland a chance to lay down weapons or leave the country. It could also help ease the worst crisis between Russia and the West since the Cold War, which was triggered by Moscow's annexation of Crimea that followed the ouster of Ukraine's pro-Russia president.