Israel says Palestinian gunmen have shot dead an Israeli and wounded another in the West Bank.
Fatal attacks on settlers have become rare under the truce
Hours later, Palestinian sources said Israeli troops killed an unarmed teenager in the Gaza Strip.
Meanwhile, the Israeli military said a Palestinian woman carrying hidden explosives on her body attempted to blow up Gaza's main crossing point.
It comes a day before the Israeli and Palestinian leaders are due to meet to discuss Israel's withdrawal from Gaza.
An Israeli army spokesman said the Israelis were in a car that was ambushed near the Jewish settlement of Hermesh in the West Bank.
The militant Islamic Jihad group said it carried out the attack to retaliate for what it called the desecration of the Koran at a prison in Israel.
The Israeli authorities have denied allegations that prison guards ripped pages of the Islamic holy book.
Witnesses quoted by AFP news agency said two Palestinian teenagers were hit by Israeli fire as they were apparently trying to cross a border fence from northern Gaza to search for work in Israel. It is not known how badly wounded the second teenager is.
Later, Israeli troops stopped a 21-year-old woman from the Jebaliya refugee camp in northern Gaza who they said was carrying 10 kg (22 pounds) of explosives at the Erez check-point.
She had been given permission to cross into Israel to have burns on her face seen to by hospital doctors, army spokeswoman Major Sharon Feingold said.
When asked to put up her hands by suspicious soldiers, she attempted to detonate the bomb, Maj Feingold added.
Overnight, Palestinian militants fired five mortar shells at Jewish settlements in the Gaza Strip, but no injuries were reported, the Israeli army also said.
The violence comes as Israeli Prime Minister Ariel Sharon and Palestinian leader Mahmoud Abbas are due to meet at Mr Sharon's Jerusalem residence.
It is their first meeting since a fragile ceasefire was agreed in February in the Egyptian Red Sea resort of Sharm el-Sheikh.
Correspondents say the latest violence puts further strain on the truce, which is seen as a crucial element in the effort to restart the Middle East peace process.
Although the talks are likely to be dominated by the Israeli withdrawal from Gaza, planned for August, Mr Sharon is expected to demand a greater crackdown on militants while Mr Abbas will seek a number of guarantees for Gaza residents after the withdrawal.