The yield on the 30-year U.S. Treasury has surged to its highest level in nearly two decades, and some strategists see scope for the selloff in long-dated government bonds to go further.

The 30-year Treasury yield, which is typically sensitive to geopolitical events, advanced more than 4 basis points to 5.311% on Monday, reaching its highest level since June 2007. Foreign holdings of Treasurys fell in June, the Treasury Department reported on Monday, with top holders U.K., China and Japan all reducing their holdings.