Pakistani President Asif Ali Zardari is set to visit Kabul on Tuesday for talks with Afghan President Hamid Karzai.

Mr. Zardari's office said Monday the two leaders will discuss issues of bilateral importance, and that Mr. Zardari will offer condolences to Mr. Karzai on the recent assassination of his brother, Ahmad Wali Karzai.

The visit comes amid heightened tensions between the two countries, following clashes involving militants along their shared border.

Pakistani officials said Tuesday mortars fired from Afghanistan killed four Pakistani soldiers in South Waziristan. Afghan officials did not immediately comment on the report.

Pakistan says militants allegedly coming from Afghan bases have killed more than 55 soldiers recently. Afghanistan accuses Pakistan of intentionally firing hundreds of rockets into its territory, killing at least 36 Afghan civilians.

Both sides deny the allegations.