Israel's military says a number of its soldiers have been "lightly injured" in northern Gaza.
Hamas also confirms there has been a clash - but blames Israel and says it remains committed to the temporary ceasefire.
It is the fifth day of the truce between Israel and Hamas, after a 48-hour extension was agreed yesterday.
Three Palestinians will be released from Israeli prisons in exchange for each Israeli hostage returned from Gaza.
A senior Hamas source in Qatar tells the BBC 10 hostages will be released on Tuesday and another 10 on Wednesday but these numbers have not been confirmed by Israel.
Meanwhile, the United Nations has used the pause in fighting to get desperately-needed aid into Gaza, but says much more is needed.
Hamas crossed the border and killed 1,200 people in Israel on 7 October, with about 240 taken hostage.
Since then, Gaza's Hamas-run health ministry says more than 14,500 people have been killed in Israel's retaliatory campaign.
