In what has become the worst confrontation between Russia and the West since the Cold War, Ukraine tried to retake the eastern town of Slaviansk sending in military helicopters, one of which was shot down by separatists.
In times of increased geopolitical risk, investors park their money in top-rated assets, with German Bunds seen among the safest in the world.
Ten-year Bund yields, the benchmark for euro zone borrowing costs, fell as low as 1.454 percent before retreating to 1.46 percent, 1 basis point lower on the day.
In another sign of normalisation in the euro zone's peripheral markets, yields on lower-rated euro zone bonds dipped as well, with Spanish 10-year yields close to breaching 3 percent for the first time in nine years.
Traders said Spanish, Italian and Irish bonds were not treated as risky assets anymore and were seen as a safer alternative to equities.
"The situation in Ukraine is getting more attention this morning ... but Europe as a whole feels OK," one trader said, adding that the prospect of a long weekend in London due to a bank holiday on Monday made investors extra cautious.
Market moves were limited before the release of a key release of U.S. jobs data.
Non-farm payrolls probably advanced by 210,000 jobs this month, stepping up from a 192,000-gain in March, according to a Reuters survey of economists.
"If payrolls are strong, the rise in U.S. yields will be much more significant than in European yields," BNP Paribas rate strategist Patrick Jacq said.
"Growth remains subdued (in Europe) and the market remains convinced the trend in inflation is on the downside."
U.S. 10-year yields were 2 basis points higher on the day at 2.63 percent, having dipped about 5 bps on Thursday, when European markets were closed.