KANDAHAR, Afghanistan — U.S. forces lost 22 soldiers in Afghanistan, mostly to roadside bombs, since Friday, marking a bloody step-up in the insurgency as a major U.S.-led offensive seeks to capture the spiritual homeland of the Taliban movement in Kandahar.

The U.S.-led International Security Assistance Force in Afghanistan said it is gaining ground against the insurgents, but violence is rising across the country, including in areas that were considered relatively safe.

Five more U.S. soldiers were killed Tuesday, while three Afghan workers for the British charity Oxfam were killed by a roadside bomb in Badakhshan, which had been one of the safer places in the country.

The coalition says that casualties are rising as they push against the strongholds of the Taliban in the south and the allied Haqqani network in the east. The majority of casualties — 60 percent — this year and in 2009 came from improvised explosive devices planted on roads and paths.

U.S. and Afghan forces are expected to begin soon an offensive in Zhari and Panjwai, southwest of Kandahar city, the last part of operation “”Hamkari,”” to secure and stabilize Kandahar province. Mullah Omar started the Taliban movement in this area in 1994, and it conquered much of the country in the two years that followed.

Of the 22 American losses since Friday, 17 were the result of IEDs, according to figures provided by the ISAF. In that period, only one non-American coalition soldier was killed.

“”It has all been in the south and the east, where most of the kinetic activity is at the moment,”” said Katie Kendrick, a spokeswoman for the ISAF in Kabul, referring to the fatalities.

The United States accounted for 55 of the 76 coalition deaths in August, which topped a painful summer for coalition forces, with 102 foreign soldiers killed in Afghanistan in June and an additional 88 in July, according to the website iCasualties, which tracks losses in Afghanistan.

Kandahar is the spiritual home of the Taliban, from where Mullah Omar had ruled until Afghan and U.S. forces toppled him from power in 2001. The province is considered to be the primary goal of the Taliban, but until this year, analysts think that coalition forces didn’t commit sufficient troops to the area.

While the other major operation in the south of Afghanistan this year — targeting the town of Marjah in Helmand province — had a defined and spectacular start, the Kandahar “”mission”” is more dispersed and less defined.

The coalition and Afghan forces say they’ve improved security in Kandahar city, though it remains a dangerous place, and gained control over most of the Arghandab valley to the north of the city. The next goal of the push, expected to start within days, in the south are the Taliban-controlled districts of Zhari and Panjwai, where there is little Afghan government presence.

“”Zhari and Panjwai are the last pieces of this problem set,”” said a senior ISAF officer, who spoke on condition of anonymity because he wasn’t authorized to speak on the record. “”Today we own about 10 percent of those areas.””

The coalition is under pressure to demonstrate progress in Afghanistan ahead of President Barack Obama’s